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]