(1):
(n.) Three, considered collectively; three in company or acting together; a set of three; three united.
(2):
(n.) 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.
(3):
(n.) A composition for three parts or three instruments.