The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Binomial \Bi*no"mi*al\, a.
   1. Consisting of two terms; pertaining to binomials; as, a
      binomial root.
      [1913 Webster]

   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.
      [1913 Webster]

   Binomial theorem (Alg.), the theorem which expresses the
      law of formation of any power of a binomial.
      [1913 Webster]

WordNet (r) 3.0 (2006):

binomial
    adj 1: of or relating to or consisting of two terms; "binomial
           expression"
    2: having or characterized by two names, especially those of
       genus and species in taxonomies; "binomial nomenclature of
       bacteria" [syn: binomial, binominal]
    n 1: (mathematics) a quantity expressed as a sum or difference
         of two terms; a polynomial with two terms

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "binomial":
   Linnaean, biaxial, bicameral, bicuspid, bifid, biform, binocular,
   binominal, bipartite, biped, bipetalous, bipinnate, bisexual,
   bivalent, classificatory, nomenclatural, onomastic, orismological,
   taxonomic, terminological, toponymic, toponymous, trinomial,
   unibivalent