quadruplet

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

(noun) one of four children born at the same time from the same pregnancy. Synonyms: quad.

(noun) a set of four similar things considered as a unit. Synonyms: quartet, quartette, quadruple.