1. [ noun ] one of four children born at the same time from the same pregnancy
Synonyms: quad
Related terms: sibling
2. [ noun ] (mathematics) the cardinal number that is the sum of three and one
Synonyms: four 4 quaternity quatern tetrad quaternary quaternion quartet foursome Little_Joe IV
Related terms: digit
3. [ noun ] a set of four similar things considered as a unit
Synonyms: quartette quartet
Related terms: set
Similar spelling:   quadruple