Twin a.
1. Being one of two born at a birth; as, a twin brother or sister.
2. Being one of a pair much resembling one another; standing in the relation of a twin to something else; -- often followed by to or with.
3. Bot. Double; consisting of two similar and corresponding parts.
4. Crystallog. Composed of parts united according to some definite law of twinning. See Twin, n., 4.
Twin boat, or Twin ship Naut., a vessel whose deck and upper works rest on two parallel hulls.
Twin crystal. See Twin, n., 4.
Twin flower Bot., a delicate evergreen plant (Linnaea borealis) of northern climates, which has pretty, fragrant, pendulous flowers borne in pairs on a slender stalk.
Twin-screw steamer, a steam vessel propelled by two screws, one on either side of the plane of the keel.