From The Collaborative International Dictionary of English v.0.48 [gcide]:
Trio \Tri"o\, n. [It., fr. L. tres, tria, three: cf. F. trio,
from the Italian. See Three.]
1. Three, considered collectively; three in company or acting
together; a set of three; three united.
[1913 Webster]
The trio were well accustomed to act together, and
were linked to each other by ties of mutual
interest. --Dickens.
[1913 Webster]
2. (Mus.)
(a) A composition for three parts or three instruments.
(b) The secondary, or episodical, movement of a minuet or
scherzo, as in a sonata or symphony, or of a march, or
of various dance forms; -- not limited to three parts
or instruments.
[1913 Webster] Triobolar
From WordNet (r) 3.0 (2006) [wn]:
trio
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: a musical composition for three performers
3: three performers or singers who perform together
4: a set of three similar things considered as a unit [syn:
trio, triad, triplet, triple]
5: three people considered as a unit [syn: trio, threesome,
triad, trinity]