noun A grammatical number referring to four (or more) things.
noun A set of points with all the combinatorial properties of a quadric (a quadric being the set of points of PG(n, q) whose coordinates satisfy a quadratic equation).
noun A set of four phrases, separated by pauses when speaking or commas when writing.
noun A foursome.
adjective Referring to four (or more) things; of, in or relating to the quadral grammatical number.