/te"trad/ , n.
1. a group of four.
2. the number four.
3. Cell Biol. a group of four chromatids formed by synapsis at the beginning of meiosis.
4. Chem. a tetravalent or quadrivalent element, atom, or group.
[ 1645-55; tetrad- (s. of tetrás ) group of four ]