Source : Webster's Revised Unabridged Dictionary (1913)

Binary \Bi"na*ry\, a. [L. binarius, fr. bini two by two, two at
   a time, fr. root of bis twice; akin to E. two: cf. F.
   binaire.]
   Compounded or consisting of two things or parts;
   characterized by two (things).

   {Binary arithmetic}, that in which numbers are expressed
      according to the binary scale, or in which two figures
      only, 0 and 1, are used, in lieu of ten; the cipher
      multiplying everything by two, as in common arithmetic by
      ten. Thus, 1 is one; 10 is two; 11 is three; 100 is four,
      etc. --Davies & Peck.

   {Binary compound} (Chem.), a compound of two elements, or of
      an element and a compound performing the function of an
      element, or of two compounds performing the function of
      elements.

   {Binary logarithms}, a system of logarithms devised by Euler
      for facilitating musical calculations, in which 1 is the
      logarithm of 2, instead of 10, as in the common
      logarithms, and the modulus 1.442695 instead of .43429448.
      

   {Binary measure} (Mus.), measure divisible by two or four;
      common time.

   {Binary nomenclature} (Nat. Hist.), nomenclature in which the
      names designate both genus and species.

   {Binary scale} (Arith.), a uniform scale of notation whose
      ratio is two.

   {Binary star} (Astron.), a double star whose members have a
      revolution round their common center of gravity.

   {Binary theory} (Chem.), the theory that all chemical
      compounds consist of two constituents of opposite and
      unlike qualities.

Compound \Com"pound\, n.
   1. That which is compounded or formed by the union or mixture
      of elements ingredients, or parts; a combination of
      simples; a compound word; the result of composition.
      --Shak.

            Rare compound of oddity, frolic, and fun.
                                                  --Goldsmith.

            When the word ``bishopric'' was first made, it was
            made as a compound.                   --Earle.

   2. (Chem.) A union of two or more ingredients in definite
      proportions by weight, so combined as to form a distinct
      substance; as, water is a compound of oxygen and hydrogen.

   Note: Every definite chemical compound always contains the
         same elements, united in the same proportions by
         weight, and with the same internal arrangement.

   {Binary compound} (Chem.). See under {Binary}.

   {Carbon compounds} (Chem.). See under {Carbon}.

Source : WordNet®

binary compound
     n : chemical compound composed of only two elements