decagon 
 noun (plural decagons)
 (geometry) A polygon with ten sides and ten angles.



decimal 
 noun
 (context, arithmetic, computing, uncountable) The number system that uses the digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9.
 (countable) A number expressed in this system.
 (informal) A decimal place.
adjective
 (context, arithmetic, computing) Concerning numbers expressed in decimal or mathematical calculations performed using decimal.

decreasing 
 verb
 Present participle of to decrease.

decrement 
 noun  A small quantity removed or lost. One of a series of regular subtractions.
verb  To decrease a value by a basic quantity unit. Opposite of increment. Typically used in computer programming. If A=3, and you decrement A, then A=2.

defective number 
 noun (plural defective numbers)
 (number theory) A deficient number.

deficient number 
 noun
 (number theory) A number that greater than the sum of all of its divisors except itself.
 The factors of 22 are 1, 2 and 11 and 22, and 1 + 2 + 11 = 14, which is less than 22, so 22 is a .

definite integral 
 noun  (mathematics) The integral of a function betwen an upper and lower limit

degenerate 
 noun
 One is degenerate, who has fallen from previous stature.
 You are a , boy. You're a disgrace to your ancestors.
adjective
 (of qualities) having deteriorated, degraded or fallen from normal, coherent, balanced and desire, desirable to an undesirable and typically abnormal
 (of a human or system) having lost good or desirable qualities
 (of an encoding or function) having multiple domain elements correspond to one element of the range
 ''The genetic code is degenerate because a single amino acid can be coded by one of several codon, codons.
 (math) a degenerate case is a limiting case in which a class of object changes its nature so as to belong to another, usually simpler, class.

degree 
 noun
 (geometry) A unit of measurement of angle equal to 1/360 of a circle's circumference.
 (physics) A unit of measurement of temperature on any of several scales, such as Celsius or Fahrenheit.
 Any of various units used to express specific gravity, bitterness, darkness, etc. in manufacturing various commodities.
 The amount that an entity possesses a certain property; proportion or extent.
 To what degree do the two accounts of the accident concur?
 An award (generally superior to a diploma but inferior to a doctorate) bestowed by a university or, in some countries, a college, as an indication of academic achievement or occasionally bestowed to honor its recipient.
 (graph theory) The number of edge, edges that a vertex takes part in.
 (mathematics) The sum of the exponents of a term; or, in the context of a polynomial, the highest degree of all its terms.

denary 
 adjective
 tenfold
 based on the number ten; decimal

denominator 
 noun
 (arithmetic) The number or expression written below the line in a fraction.

dense 
 adjective (denser, densest)
 Having relatively high density.
 Compact; crowded together.
 Thick; difficult to penetrate.
 Opaque; allowing little light to pass through.
 Obscure, or difficult to understand.
 Of a person, slow to comprehend; of low intelligence.

dependent variable 
 noun
 (algebra) In an equation, the variable whose value depends on one or more variables in the equation.
 In the equation z = x^{2} + y, z is the dependent variable.
 In sciences, an outcome measured to see the effectiveness of the treatment.

derivative 
 noun (plural: derivatives)
 Something derive, derived.
 A word that derives from another one.
 (finance) A financial instrument whose value depends on the valuation of an underlying asset; such as a warrant, an option etc.
 (chemistry) A chemical derived from another.
 (calculus) The derived function of a function.
 The derivative of <math>f(x) = x^2</math> is <math>f'(x) = 2x</math>
 (calculus) The value of this function for a given value of its independent variable.
 The derivative of <math>f(x) = x^2</math> at x = 3 is <math>f'(3) = 2
adjective  Imitative of the work of someone else
 (copyright law) Referring to a work, such as a translation or adaptation, based on another work that may be subject to copyright restrictions
 Having a value that depends on an underlying asset of variable value
 Lacking originality

describe 
 verb (describ, ing)
 (transitive) To represent in words.
 The feeling is difficult to , but not unpleasant.
 (transitive) (mathematics) To give rise to a geometrical structure.
 The function describes a very complex surface.

description 
 noun
 Result of putting in words; a synopsis of what something is.
 Procedure of putting in words.

descriptive geometry 
 noun
 A graphical protocol which creates threedimensional virtual space on a twodimensional plane.

determinant 
 noun
 A determine, determining factor; an element that determines the nature of something
 (linearalg) The unique scalar function over square matrix, matrices which is distributive over matrix multiplication, multilinear in the rows and columns, and takes the value of 1 for the unit matrix. Abbreviation: det
 (biology) A substance that causes a cell to adopt a particular fate.

determine 
 verb (determin, ing)
 To set the limits of.
 To ascertain definitely; to figure out.

develop 
 verb
 To progress.
 Let's see how things and then make our decision.
 To progress through a sequence of stages.
 Isabel developed from a tropical depression to a tropical storm to a hurricane.
 An embryo develops into a fetus and then into an infant.
 To create.
 I need to a plan for the next three weeks.
 To bring out images latent in photographic film.
 Please this roll of film.
 (context, Chess) To place ones pieces actively.
 I need to my whitesquare bishop.
 (context, snooker, pool) To cause a ball to become more open and available to be played on later. Usually by moving it away from the cushion, or by opening a pack.

developable surface 
 noun  A surface (in more than two dimensions, a plane is trivially developable) that can be flattened into a plane without distortion.
category:Geometry
category:Cartography

diagonal 
 noun
 something arranged diagonally or obliquely
 a line or cut across a fabric that is not at right angles to a side of the fabric
 a punctuation mark used to separate related items of information
 (geometry) a diagonal line or plane
adjective
 (geometry) joining, Joining two nonadjacent vertices (of a polygon or polyhedron).
 Having a slanted or oblique direction, lines or markings.
 Pertaining to the front left and back right (or the front right and back left) legs of a quadruped.

diagonal matrix 
 noun  (linearalg) A matrix where only the entry, entries on the main diagonal are nonzero.

diagram 
 noun
 A plan, drawing, sketch or outline to show how something works, or show the relationships between the parts of a whole; electrical diagrams show device interconnections see schematics.
 (mathematics) a graphic representation of an algebraic or geometric relationship
 A graph or chart
verb (diagrams, diagraming or diagramming, diagramed or diagrammed)
 (transitive) To represent or indicate something using a diagram.

diameter 
 noun (plural diameters)
 (geometry) Any straight line between two points on the circumference of a circle that passes through the centre/center of the circle.
 (geometry) The length of such a line.
 (graphtheory) The maximum eccentricity over all vertices in a graph.

diametral 
 adjective
 of, relating to, or measured across a diameter
 contrary; diametrically opposed

Diamond 
 proper noun
 (given name, female) of modern usage, from the name of the gem.

differential 
 noun
 the differential gear in an automobile etc
 a qualitative or quantitative difference between similar or comparable things
 (mathematics) an infinitesimal change in a variable, or the result of differentiation
adjective
 of, or relating to a difference
 dependent on, or making a difference; distinctive
 having differences in speed or direction of motion
 (mathematics) of, or relating to differentiation, or the differential calculus

differential calculus 
 noun (uncountable)
 (calculus) The calculus that deals with instantaneous rate of change, rates of change.

differential equation 
 noun
 (mathematics) an equation involving the derivatives of a function

differentiate 
 verb (differentiat, ing)
 (transitive) To show, or be the distinction between two things
 1933: The mass of the rich and poor are differentiated by their incomes and nothing else, and the average millionaire is only the average dishwasher dressed in a new suit.  George Orwell, Down and Out in Paris and London, Ch. XXII, pg. 120 (Harvest / Harcourt paperback edition).
 (intransitive) To perceive the difference between things; to discriminate
 (context, transitive, intransitive) To modify, or be modified.
 (context, transitive, mathematics) To calculate the derivative of a function.
 (context, transitive, mathematics) To calculate the differential of a function of multiple variables.
 (context, intransitive, biology) To produce distinct organs or to achieve specific functions by a process of development called differentiation.

digit 
 noun
 A finger or toe.
 (arithmetic) A numeral that can be combined with others to write larger numbers, and that cannot itself be split into other numerals.
 The digits of the decimal number system are 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9, and those in the hexadecimal number system are those in the decimal system along with A, B, C, D, E and F.
 The number 2307 has four digits: the thousands digit is 2; the hundreds digit is 3; the tens digit is 0; and the units digit is 7.
 (context, slang, UK, in plural) One's phone number.
 That girl likes me — she gave me her digits.

digital 
 adjective (notcomp)
 Having to do with digits (fingers or toes); performed with a finger.
 Property of representing values as discrete numbers rather than a continuous spectrum.
 digital computer, digital clock
 Of or relating to computers or the Computer Age.

dihedral 
 noun
 (mathematics) An angle between two plane surfaces
 (aeronautics) The upward slope of an aircraft's wing
 (chemistry) The angle between pairs of chemical bonds separated by a third bond
adjective
 (mathematics) Consisting of, relating to or contained between two plane surfaces.

directed 
 verb
 (past of, direct)
adjective
 In a manner emphasizing one's point of view.

directly 
 adverb
 In a direct manner; in a straight line or course.
 In a straightforward way; without anything intervene, intervening; not by secondary, but by direct means.
 Without circumlocution or ambiguity; absolutely; in express terms.
 exactly, Exactly; just.
 straightforwardly, Straightforwardly; honestly.
 (oldfashioned) immediately
 (context, Midland South) Soon; later; when it becomes convenient
 We'll go to the store , but first I need to finish sweeping.

discontinuity 
 noun
 a lack of continuity, regularity or sequence; a break or gap
 (geology) a subterranean interface at which seismic velocities change
 (mathematics) a point in the range of a function at which it is undefined or not continuous

discontinuous 
 adjective
 having breaks or interruptions; intermittent
 (mathematics) having at least one discontinuity

discriminant 
 noun (plural discriminants)
 (algebra) An expression that gives information about the roots of a polynomial; for example, the expression D = b^{2}  4ac determines whether the roots of the quadratic equation ax^{2} + bx + c = 0 are real and distinct (D > 0), real and equal (D = 0) or complex (D < 0).

disk 
 noun
 A thin, flat, circular plate or similar object.
 A coin is a of metal.
 (figurative) Something resembling a disk.
 Venus' cut off light from the Sun.
 (dated) A vinyl phonograph / gramophone record.
 Turn the over, after it has finished.
 (computing) A floppy disk  removable magnetic medium or a hard disk  fixed, persistent digital storage.
 He still uses floppy disks from 1979.
 (computing, nonstandard) A disc  either a CDROM, an audio CD, a DVD or similar removable storage medium.
 She burned some disks yesterday to back up her computer.

distance 
 noun
 (countable) The amount of space between two points, usually geographical points, usually (but not necessarily) measured along a straight line.
 The to Petersborough is thirty miles.
 (context, uncountable, figurative) The entire amount of space to the objective.
 He had promised to perform this task, but did not go the .
 (context, uncountable, figurative) A considerable amount of space.
 The friendship did not survive the row: they kept each other at a .
verb (distanc, ing)
 To move away from someone or something.

distribution 
 noun
 a distribution or being distributed; specifically, (a) apportionment by law (of funds, property, etc.), (b) the process by which commodities get to final consumers, including storing, selling, shipping, and advertising, (c) frequency of occurrence or extent of existence
 anything distributed; portion; share
 the result of distributing; arrangement
 (statistics) the relative arrangements of the elements of a statistical population based on some criterion, as frequency, time, or location

diverge 
 verb (diverg, ed)
 (intransitive) to run apart; to tend into different directions
 (intransitive) (mathematics) (of a sequence) to have no limit

divergent 
 adjective
 Growing further apart; diverge, diverging.
 (mathematics): describing a series which does not converge, i.e., approach a limit.

divide 
 noun
 A thing that divides.
 Stay on your side of the , please.
 An act of dividing.
 The left most of the good land on my share of the property.
 A distancing between two people or things.
 There is a great between us.

dividend 
 noun
 (arithmetic) A number or expression that is to be divided by another. Eg. in "42 í· 3" the dividend is the 42.
 (finance) A pro rata payment of money by a company to its shareholders, usually made periodically (eg. quarterly or annually).

divisibility 
 noun
 (arithmetic) The property of being divisible by a particular integer.

division 
 noun
 (uncountable) The act or process of dividing anything.
 Each of the separate parts of something resulting from division.
 (arithmetic) (uncountable) The process of divide, dividing a number by another.
 (arithmetic) A calculation that involves this process.
 I've got ten divisions to do for my homework.
 A large military unit, usually made up of two or three brigades.
 A section of a large company.
 (context, biology, taxonomy) A rank (Latin divisio) below kingdom and above class, particularly used of plant, plants or fungus, fungi, also (particularly of animals) called a phylum; a taxon at that rank
 Magnolias belong to the Magnoliophyta.
 A disagreement; a difference of viewpoint between two sides of an argument.
 (music) A florid instrumental variation of a melody in the 17th and 18th centuries, originally conceived as the dividing of each of a succession of long notes into several short ones.
 (music) A set of pipes in a pipe organ which are independently controlled and supplied.
 A concept whereby a common group of debtors are only responsible for their proportionate sum of the total debt.

division sign 
 noun (plural division signs)
 (mathematics) Any symbol (in particular ÷ or / ) used to denote the operation of division.

divisor 
 noun (plural divisors)
 (arithmetic) A number or expression that another is to be divided by. Eg. in "42 í· 3" the divisor is the 3.

dodecagon 
 noun
 (geometry) A polygon with twelve sides and twelve angles.

dot product 
 noun (plural dot products)
 (vector) A scalar product.

duality 
 noun
 A classification into two subclasses or opposed parts.
 (projective geometry) The interchangeability of points and planes.
 (mathematics), (physics) The mathematical equivalence of two seemingly different theoretical descriptions of a physical system

dual space 
 noun  (mathematics) The vector space which comprises the set of linear transformations of a given vector space into its scalar field


dyad 
 noun
 A set of two different elements.
 1924: ARISTOTLE. Metaphysics. Translated by W. D. Ross. Nashotah, Wisconsin, USA: The Classical Library, 2001. Available at: <http://www.classicallibrary.org/aristotle/metaphysics/>. Book 1, Part 6.
 : positioning a and constructing the infinite out of great and small, instead of treating the infinite as one, is pucliar to him;
 (music) any set of two different pitch classes.

dyadic 
 adjective  Pertaining to the number two; of two parts or elements.
