Source : Webster's Revised Unabridged Dictionary (1913)

Counterpart \Coun"ter*part`\ (koun"t?r-p?rt`), n.
   1. A part corresponding to another part; anything which
      answers, or corresponds, to another; a copy; a duplicate;
      a facsimile.

            In same things the laws of Normandy agreed with the
            laws of England, so that they seem to be, as it
            were, copies or counterparts one of another. --Sir
                                                  M. Hale.

   2. (Law) One of two corresponding copies of an instrument; a
      duplicate.

   3. A person who closely resembles another.

   4. A thing may be applied to another thing so as to fit
      perfectly, as a seal to its impression; hence, a thing
      which is adapted to another thing, or which supplements
      it; that which serves to complete or complement anything;
      hence, a person or thing having qualities lacking in
      another; an opposite.

            O counterpart Of our soft sex, well are you made our
            lords.                                --Dryden.

Source : WordNet®

counterpart
     n 1: a person or thing having the same function or
          characteristics as another [syn: {opposite number}, {vis-a-vis}]
     2: a duplicate copy [syn: {similitude}, {twin}]