Tetrad

n.	1.	The number four; a collection of four things; a quaternion.
	2.	(Chem.) A tetravalent or quadrivalent atom or radical; as, carbon is a tetrad.

Noun

1.

tetrad - the cardinal number that is the sum of three and one Synonyms: IV, Little Joe, quadruplet, quartet, quatern, 4, four, quaternion, quaternity, foursome, quaternary

4, digit, figure, four, foursome, IV, Little Joe, quadruplet, quartet, quatern, quaternary, quaternion, quaternity