From The Collaborative International Dictionary of English v.0.48 [gcide]:
Triplet \Trip"let\, n. [From Triple.]
1. A collection or combination of three of a kind; three
united.
[1913 Webster]
2. (Poetry) Three verses rhyming together.
[1913 Webster]
3. (Mus.) A group of three notes sung or played in the tree
of two.
[1913 Webster]
4. pl. Three children or offspring born at one birth.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
triplet
n 1: the cardinal number that is the sum of one and one and one
[syn: three, 3, III, trio, threesome, tierce,
leash, troika, triad, trine, trinity, ternary,
ternion, triplet, tercet, terzetto, trey, {deuce-
ace}]
2: one of three offspring born at the same time from the same
pregnancy
3: a set of three similar things considered as a unit [syn:
trio, triad, triplet, triple]