Source : Webster's Revised Unabridged Dictionary (1913)

Binomial \Bi*no"mi*al\, n. [L. bis twice + nomen name: cf. F.
   binome, LL. binomius (or fr. bi- + Gr. ? distribution ?). Cf.
   {Monomial}.] (Alg.)
   An expression consisting of two terms connected by the sign
   plus (+) or minus (-); as, a + b, or 7 - 3.

Binomial \Bi*no"mi*al\, a.
   1. Consisting of two terms; pertaining to binomials; as, a
      binomial root.

   2. (Nat. Hist.) Having two names; -- used of the system by
      which every animal and plant receives two names, the one
      indicating the genus, the other the species, to which it
      belongs.

   {Binomial theorem} (Alg.), the theorem which expresses the
      law of formation of any power of a binomial.

Source : WordNet®

binomial
     adj 1: relating to binomials; "binomial expression"
     2: consisting of two names or terms; "binomial nomenclature"

binomial
     n : a quantity expressed as a sum or difference of two terms