Definition of: twin

(twin) noun
1. One of two young produced at the same birth.
2. The counterpart or exact mate of another.
3. An intergrowth of two or more crystals of the same substance according to some definite law, a single plane or axis usually being common to the different individuals.
—the Twins Castor and Pollux, the two brightest stars in the constellation Gemini; also, the constellation.
—adjective
1. Being, or standing in the relation of, a twin or twins.
2. Consisting of, forming, or being one of a pair of similar and closely related objects; double; twofold.
—the Twin Cities St. Paul and Minneapolis.
—v. twinned, twin·ning v.i.
1. To bring forth twins.
2. To be matched or equal; agree.
3. Archaic To be born as a twin.
—v.t.
4. To bring forth as twins.
5. To couple; match.
6. Scot. To separate: also twine (twīn). [Fusion of OE twinn, getwinn (<twi- <twa two) and ON tvinnr, tvennr double]