from
The Collaborative International Dictionary of English v.0.48
Twin \Twin\ (tw[i^]n), a. [OE. twin double, AS. getwinne two and
two, pl., twins; akin to D. tweeling a twin, G. zwilling,
OHG. zwiniling, Icel. tvennr, tvinnr, two and two, twin, and
to AS. twi- two. See {Twice}, {Two}.]
1. Being one of two born at a birth; as, a twin brother or
sister.
[1913 Webster]
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. --Shak.
[1913 Webster]
3. (Bot.) Double; consisting of two similar and corresponding
parts.
[1913 Webster]
4. (Crystallog.) Composed of parts united according to some
definite law of twinning. See {Twin}, n., 4.
[1913 Webster]
{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.
[1913 Webster]