a. [ L. trinoctialis for three nights; tri- (see Tri-) + nox, noctis, night. ] Lasting during three nights; comprising three nights. [ 1913 Webster ]

n. [ Pref. tri- + -nomial as in binomial: cf. F. trinôme. ] (Math.) A quantity consisting of three terms, connected by the sign + or -; as, x + y + z, or ax + 2b - c2. [ 1913 Webster ]

a. 1. (Math.) Consisting of three terms; of or pertaining to trinomials; as, a trinomial root. [ 1913 Webster ]

2. (Nat. Hist.) Consisting of, or involving the use of, three terms; as, a trinomial systematic name specifying the genus, species, and variety. [ Webster 1913 Suppl. ]