tri·no·mi·al / trīˈnōmēəl/ • adj. 1. (of an algebraic expression) consisting of three terms.2. Biol. a systematic name for a taxon consisting of three terms of which the first is the name of the genus, the second that of the species, and the third that of the subspecies or variety.• n. 1. an algebraic expression of three terms.2. Biol. a trinomial taxonomic name.