The Collaborative International Dictionary of English v.0.48:

Depreciation \De*pre`ci*a"tion\
   (d[-e]*pr[=e]`sh[i^]*[=a]"sh[u^]n), n. [Cf. F.
   d['e]pr['e]ciation.]
   1. The act of lessening, or seeking to lessen, price, value,
      or reputation.
      [1913 Webster]

   2. The falling of value; reduction of worth. --Burke.
      [1913 Webster]

   3. the state of being depreciated.
      [1913 Webster]

WordNet (r) 3.0 (2006):

depreciation
    n 1: a decrease in price or value; "depreciation of the dollar
         against the yen" [ant: appreciation]
    2: decrease in value of an asset due to obsolescence or use
       [syn: depreciation, wear and tear]
    3: a communication that belittles somebody or something [syn:
       disparagement, depreciation, derogation]

Moby Thesaurus II by Grady Ward, 1.0:

186 Moby Thesaurus words for "depreciation":
   abatement, ablation, abridgment, agio, alleviation, allowance,
   attenuation, attrition, backbiting, backstabbing, bank discount,
   belittlement, belittling, break, breakage, calumny, cash discount,
   chain discount, charge-off, cheapening, comedown, concession,
   consumption, contempt, contraction, curtailment, cut, cutting,
   dampening, damping, debasement, decadence, decadency, declension,
   declination, decline, decrease, decrement, decrescence, decrial,
   deduction, defamation, deflation, deformation, degeneracy,
   degenerateness, degeneration, degradation, demotion, denigration,
   depletion, depravation, depravedness, deprecation, depression,
   derogation, descent, deterioration, detraction, devaluation,
   devolution, diminishment, diminution, dip, disapproval,
   discommendation, discount, discrediting, disgrace, disparagement,
   dispraise, dissipation, disvaluation, dive, downtrend, downturn,
   downward mobility, downward trend, drain, drawback, drop, dying,
   dying off, ebb, effeteness, erosion, evaporation, exhaustion,
   expenditure, extenuation, extraction, fade-out, fading, failing,
   failure, failure of nerve, faint praise, fall, falling-off,
   impairment, impoverishment, indignity, involution, kickback,
   knocking, languishment, lapse, leakage, lessening, letup,
   loss of tone, lowering, lukewarm support, markdown,
   miniaturization, minimization, minimizing, misestimation,
   misprision, misprizal, misprizing, mitigation, nose dive, penalty,
   penalty clause, percentage, plummet, plummeting, plunge, premium,
   price cut, price fall, price reduction, price-cut, putting down,
   rebate, rebatement, reduction, refund, regression, relaxation,
   remission, retraction, retrenchment, retrocession, retrogradation,
   retrogression, ridicule, rollback, sag, sagging, salvage,
   scaling down, scandal, setoff, shortening, shrinkage, simplicity,
   slander, slash, slighting, slippage, slump, sour grapes,
   subtraction, tale, tare, time discount, trade discount, tret,
   truncation, underestimate, underestimation, underrating,
   underreckoning, underselling, undervaluation, using, using up,
   wane, wastage, waste, weakening, wearing, wearing away,
   write-off