Trio

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

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.