TWIN

I. noun Etymology: Middle English, from ~ twofold Date: 14th century 1. either of two offspring produced at a birth, Gemini , one of two persons or things closely related to or resembling each other, a compound crystal composed of two adjoining crystals or parts of crystals of the same kind that share a common plane of atoms, ~ship noun II. verb (~ned; ~ning) Date: 14th century transitive verb to bring together in close association ; couple , duplicate , match , intransitive verb to bring forth ~s, to grow as a ~ crystal, III. adjective Etymology: Middle English, twofold, double, from Old English ~n; akin to Old Norse tvinnr two by two, Old English twā two Date: 1593 born with one other or as a pair at one birth , 2. made up of two similar, related, or connected members or parts ; double , paired in a close or necessary relationship ; matching, having or consisting of two identical units, being one of a pair