The Collaborative International Dictionary
Quadrinomial
Quadrinomial \Quad`ri*no"mi*al\, n. [Quadri- + nomial, as in binomial: cf. F. quadrin[^o]me.] (Alg.) A polynomial of four terms connected by the signs plus or minus.
Wiktionary
quadrinomial
a. Consisting of four names or parts or terms. n. (context algebra English) An expression consisting of four terms.