The Collaborative International Dictionary of English v.0.48:

Depreciate \De*pre"ci*ate\, v. i.
   To fall in value; to become of less worth; to sink in
   estimation; as, a paper currency will depreciate, unless it
   is convertible into specie.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Depreciate \De*pre"ci*ate\ (d[-e]*pr[=e]"sh[i^]*[=a]t), v. t.
   [imp. & p. p. Depreciated
   (d[-e]*pr[=e]"sh[i^]*[=a]`t[e^]d); p. pr. & vb. n.
   Depreciating (d[-e]*pr[=e]"sh[i^]*[=a]`t[i^]ng).] [L.
   depretiatus, depreciatus, p. p. of depretiare, -ciare, to
   depreciate; de- + pretiare to prize, fr. pretium price. See
   Price.]
   To lessen in price or estimated value; to lower the worth of;
   to represent as of little value or claim to esteem; to
   undervalue. --Addison.
   [1913 Webster]

         Which . . . some over-severe philosophers may look upon
         fastidiously, or undervalue and depreciate. --Cudworth.
   [1913 Webster]

         To prove that the Americans ought not to be free, we
         are obliged to depreciate the value of freedom itself.
                                                  --Burke.

   Syn: To decry; disparage; traduce; lower; detract; underrate.
        See Decry.
        [1913 Webster]

WordNet (r) 3.0 (2006):

depreciate
    v 1: belittle; "The teacher should not deprecate his student's
         efforts" [syn: deprecate, depreciate, vilipend]
    2: lower the value of something; "The Fed depreciated the dollar
       once again" [ant: appreciate, apprise, apprize]
    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:

149 Moby Thesaurus words for "depreciate":
   abate, ablate, abrade, abridge, abstract, abuse, allow, bate,
   beat down, belittle, break, bring down, bring into discredit,
   bring low, charge off, cheapen, compress, consume, cry down,
   curtail, cut, cut back, cut down, cut prices, damp, dampen,
   de-emphasize, debase, decline, decrease, decry, deduct, deflate,
   degrade, denigrate, deplete, deprecate, depress, deride, derogate,
   derogate from, despise, detract, detract from, devaluate, devalue,
   diminish, disapprove of, discommend, discount, discredit, disdain,
   disesteem, disgrace, disparage, dispraise, dissipate, disvalue,
   dive, downgrade, downplay, drain, dribble away, dwindle, eat away,
   erode, extract, fall, fall in price, file away, give way,
   hold in contempt, impair, jew down, kick back, knock, leach,
   lessen, lower, make allowance, make light of, make little of,
   make nothing of, mark down, minimize, misestimate, misprize,
   nose-dive, pare, play down, plummet, plunge, purify, put down,
   rebate, reduce, refine, reflect discredit upon, refund, remove,
   retrench, ridicule, roll back, rub away, run down, sag, scale down,
   sell short, set at naught, set little by, shave, shorten, shrink,
   shrug off, simplify, slash, slight, slump, soften, speak ill of,
   squander, step down, subduct, submit to indignity, subtract,
   take a premium, take away, take from, take off, talk down, thin,
   thin out, think little of, think nothing of, trim, tune down,
   underestimate, underplay, underprize, underrate, underreckon,
   undervalue, waste, wear, wear away, weed, withdraw, write down,
   write off