WordNet (r) 3.0 (2006):

devaluate
    v 1: remove the value from; deprive of its value [syn:
         devalue, devaluate]
    2: 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:

38 Moby Thesaurus words for "devaluate":
   beat down, break, cheapen, circulate, cut, cut prices, decline,
   decry, deflate, demonetize, depreciate, devalue, dive, fall,
   fall in price, give way, issue, jew down, lower, mark down,
   nose-dive, pare, plummet, plunge, reduce, reissue, remonetize,
   revalue, sag, shave, slash, slump, trim, underrate, undervalue,
   utter, write, write off