In school maths, a binomial is an expression made of two parts joined by plus or minus. 3x + 4y is a binomial. So is x − 7. Even 5 + 2 counts, because it still has two terms. One piece by itself, like 3x, is a monomial. Three pieces, like x² + 2x + 1, is a trinomial. Polynomial is the family name for these 'many-term' expressions; a binomial is the two-term kind. You meet binomials when you multiply them, and in the binomial theorem, a pattern for raising a two-part expression to a power, like (x + 1)⁵. The word belongs in the classroom and the textbook, not on the bus. Though actually, the same word walks into biology. Scientists name living things with two names, a group name and a species name: Homo sapiens. That two-name system is also called binomial, because the idea is 'two names'. If you see the word in a science book about animals, that is why; the maths sense is the one this entry is for. The history is a bit cloudy. Late Latin had binōmium; English added -al. A 12th-century translator, Gerard of Cremona, used the Latin word when working from Arabic on Euclid, matching a Greek phrase that means 'from two names'. Where binōmium itself came from, scholars are not sure — perhaps Latin nōmen, 'name', perhaps another path. On the surface, English now feels it as bi- 'two' + -nomial 'name/term'.