unary 

adjective
 Consisting of or involving a single element or component.

(mathematics) (Of a function) which takes exactly one argument; whose domain has dimension 1.

(programming) (Of a function, procedure, etc.) which takes exactly one input.


unconditional 

adjective
absolute, and without conditions, limitations, reservations or qualifications
 We demand your surrender.

undecagon 

noun (pluralundecagons)

(geometry) A polygon with eleven sides and eleven angles.

uneven 

adjective
 Not even
 Not level or smooth
 Not uniform
 Varying in quality

uniform 

noun
 A distinctive outfit as a means of identifying members of a group.

Phonetic equivalent for the letter U in the ICAO spelling alphabet, informally known as the NATO phonetic alphabet.
adjective
 unvarying, Unvarying; all the same.
 consistent, Consistent; conforming to one standard.

unilateral 

adjective
 done by one side only
 affecting only one side of the body
 binding or affecting one party only

unit circle 

noun (pluralunit circles)

(geometry) A circle of radius 1.

(trigonometry) (the unit circle) The circle of radius 1 with centre at the origin, used in defining trigonometric functions.

Universe 

proper nounthe Universe
 The sum of everything that exists in the cosmos, including time and space itself.
 Powerful telescopes look far back into the distant reaches of the visible universe.

unknown 

noun
 In algebra, a variable (usually x, y or z) whose value is to be found.
 Any fact or place about which nothing is known. (as in the phrase "into the unknown")
adjective
 Not known; unidentified; not well known.
