[tri.no.mi.al] n [tri- + -nomial (as in binomial)] (1674) 1: a polynomial of three terms
2: a biological taxonomic name of three terms of which the first designates the genus, the second the species, and the third the subspecies or variety
[2]trinomial adj (ca. 1704) 1: consisting of three mathematical terms
2: of, relating to, or being a biological trinomial