Source : Webster's Revised Unabridged Dictionary (1913)

Whiten \Whit"en\, v. i. [imp. & p. p. {Whitened}; p. pr. & vb.
   n. {Whitening}.] [OE. whitenen; cf. Icel. hv[=i]tna.]
   To grow white; to turn or become white or whiter; as, the
   hair whitens with age; the sea whitens with foam; the trees
   in spring whiten with blossoms.

Whiten \Whit"en\, v. t.
   To make white; to bleach; to blanch; to whitewash; as, to
   whiten a wall; to whiten cloth.

         The broad stream of the Foyle then whitened by vast
         flocks of wild swans.                    --Macaulay.

   Syn: See {Blanch}.

Source : WordNet®

whiten
     v : turn white; "This detergent will whiten your laundry" [syn:
         {white}] [ant: {blacken}]