adjective

1. Having four sides (as a tetragon); quadrilateral.
2. (crystallography) Having two equal axes and one unequal, and all angles 90°.

verb

1. (past of, truncate)

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noun

1. Either of two people (or, less commonly, animals) who shared the same uterus at the same time; one who was born at the same birth as a sibling.
2. Either of two similar or closely related objects, entities etc.

verb (twin, n, ing)

1. (italbrac, transitive, obsolete except Scotland) To separate, divide.
2. (italbrac, intransitive, obsolete except Scotland) To split, part; to go away, depart.
3. (usually in the passive) To join, unite; to form links between (now especially of two places in different countries).

Placetown in England is twinned with Machinville in France.

1. (intransitive) To give birth to twins.

adjective

1. Forming a pair of twins.

the twin boys

1. Forming a matched pair.

twin socks

noun

1. action of the verb to twin
2. giving birth to twins
3. the pairing of similar objects (such as towns)
4. (context, mineralogy) the formation of twin crystals
5. (context, transportation) the conversion of a road into a dual carriageway

adjective

1. biparous