The Collaborative International Dictionary of English v.0.48:

Cleanser \Cleans"er\ (kl[e^]nz"[~e]r), n. [AS. cl[=ae]nsere.]
   One who, or that which, cleanses; especially, a detergent or
   other preparation used for cleaning. --Arbuthnot.

   Syn: cleansing agent, cleaner.
        [1913 Webster]

WordNet (r) 3.0 (2006):

cleanser
    n 1: a preparation used in cleaning something [syn: cleansing
         agent, cleanser, cleaner]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "cleanser":
   Carbona, abstergent, benzine, bleach, borax, carbon tet,
   carbon tetrachloride, cathartic, cleaner, cleaning agent,
   cleaning solvent, cleansing cream, cold cream, cream, dentifrice,
   depurant, detergent, diuretic, emetic, enema, holystone, lotion,
   mouthwash, nauseant, pumice stone, purgative, purge, purifier,
   rinse, sal soda, shampoo, soap, soda, solvent, synthetic detergent,
   tooth powder, toothpaste, wash, washing soda