The Collaborative International Dictionary of English v.0.48:

Appreciation \Ap*pre`ci*a"tion\, n. [Cf. F. appr['e]ciation.]
   1. A just valuation or estimate of merit, worth, weight,
      etc.; recognition of excellence.
      [1913 Webster]

   2. Accurate perception; true estimation; as, an appreciation
      of the difficulties before us; an appreciation of colors.
      [1913 Webster]

            His foreboding showed his appreciation of Henry's
            character.                            --J. R. Green.
      [1913 Webster]

   3. A rise in value; -- opposed to depreciation.
      [1913 Webster]

WordNet (r) 3.0 (2006):

appreciation
    n 1: understanding of the nature or meaning or quality or
         magnitude of something; "he has a good grasp of accounting
         practices" [syn: appreciation, grasp, hold]
    2: delicate discrimination (especially of aesthetic values);
       "arrogance and lack of taste contributed to his rapid
       success"; "to ask at that particular time was the ultimate in
       bad taste" [syn: taste, appreciation, discernment,
       perceptiveness]
    3: an expression of gratitude; "he expressed his appreciation in
       a short note"
    4: a favorable judgment; "a small token in admiration of your
       works" [syn: admiration, appreciation]
    5: an increase in price or value; "an appreciation of 30% in the
       value of real estate" [ant: depreciation]