Source : Webster's Revised Unabridged Dictionary (1913)

Adulterant \A*dul"ter*ant\, n. [L. adulterans, p. pr. of
   adulterare.]
   That which is used to adulterate anything. -- a.
   Adulterating; as, adulterant agents and processes.

Source : WordNet®

adulterant
     adj : making impure or corrupt by adding extraneous materials;
           "the adulterating effect of extraneous materials" [syn:
            {adulterating}] [ant: {purifying}]
     n : any substance that adulterates (lessens the purity or
         effectiveness of a substance); "it is necessary to remove
         the adulterants before use" [syn: {adulterator}]