[n] the cardinal number that is the sum of three and one
[n] last 2 million years
[adj] coming next after the third and just before the fifth in position or time or degree or magnitude; "the quaternary period of geologic time extends from the end of the tertiary period to the present"
[adj] consisting of or especially arranged in sets of four; "quaternate leaves"; "a quaternary compound"
Synonyms
4, 4th, Age of Man, four, foursome, fourth, IV, Little Joe, multiple, ordinal, quadruplet, quartet, quatern, Quaternary period, quaternate, quaternion, quaternity, tetrad