—adj. 1. consisting of four.
2. arranged in fours.
3. (cap.) Geol.noting or pertaining to the present period of earth history, forming the latter part of the Cenozoic Era, originating about 2 million years ago and including the Recent and Pleistocene Epochs. See table under geologic time. 4. Metall.(of an alloy) having four principal constituents.
—n. 1. a group of four.
2. the number four.
3. (cap.) Geol.the Quaternary Period or System.