Source : Webster's Revised Unabridged Dictionary (1913)

Whitener \Whit"en*er\, n.
   One who, or that which, whitens; a bleacher; a blancher; a
   whitewasher.

Source : WordNet®

whitener
     n : an agent that makes things white or colorless [syn: {bleaching
         agent}, {bleach}, {blanching agent}]