1. A group or set of three of one kind.

2. One of three children born at one birth.

3. A group of three lines of verse.

4. Music A group of three notes having the time value of two notes of the same kind. Also called tercet.

5. Physics A multiplet with three components.

6. Genetics A unit of three successive nucleotides in a molecule of DNA or RNA that codes for a specific amino acid; a codon or anticodon.