Source : Webster's Revised Unabridged Dictionary (1913)

Oxidizer \Ox"i*di`zer\, n. (Chem.)
   An agent employed in oxidation, or which facilitates or
   brings about combination with oxygen; as, nitric acid,
   chlorine, bromine, etc., are strong oxidizers.

Source : WordNet®

oxidizer
     n : a substance that oxidizes another substance [syn: {oxidant},
          {oxidiser}, {oxidizing agent}]