(1):
(n.) A quantity consisting of three terms, connected by the sign + or -; as, x + y + z, or ax + 2b - c2.
(2):
(a.) Consisting of, or involving the use of, three terms; as, a trinomial systematic name specifying the genus, species, and variety.
(3):
(a.) Consisting of three terms; of or pertaining to trinomials; as, a trinomial root.