WordNet (r) 3.0 (2006):

devalue
    v 1: remove the value from; deprive of its value [syn:
         devalue, devaluate]
    2: lower the value or quality of; "The tear devalues the
       painting"
    3: lose in value; "The dollar depreciated again" [syn:
       depreciate, undervalue, devaluate, devalue] [ant:
       appreciate, apprise, apprize, revalue]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "devalue":
   adulterate, alloy, canker, cheapen, circulate, coarsen, confound,
   contaminate, corrupt, debase, debauch, decry, defile, deflower,
   degenerate, degrade, demonetize, denature, deprave, desecrate,
   despoil, devaluate, distort, infect, issue, lower, mark down,
   misuse, pervert, poison, pollute, prostitute, ravage, ravish,
   reissue, remonetize, revalue, taint, twist, ulcerate, underrate,
   undervalue, utter, violate, vitiate, vulgarize, warp, write,
   write off