- four, 4, IV, tetrad, quatern, quaternion, quaternary, quaternity, quartet, quadruplet, foursome, Little Joe - the cardinal number that is the sum of three and one
--1 is a kind of digit, figure
- quadruplet, quad - one of four children born at the same time from the same pregnancy
--2 is a kind of sibling, sib
- quartet, quartette, quadruplet - a set of four similar things considered as a unit
--3 is a kind of set