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1550s (n.); 1560s (adj.), from Late Latin binomius "having two personal names," a hybrid from bi- (see bi-) + nomius, from nomen (see name (n.)). Taken up 16c. in the algebraic sense "consisting of two terms."
binomial bi·no·mi·al (bī-nō'mē-əl)adj. Consisting of two terms or names, such as the genus and species names of organisms. n. A taxonomic name used in binomial nomenclature.