The Collaborative International Dictionary of English v.0.48:

deprecate \dep"re*cate\ (d[e^]p"r[-e]*k[=a]t), v. t. [imp. & p.
   p. Deprecated (-k[=a]`t[e^]d); p. pr. & vb. n.
   Deprecating (-k[=a]`t[i^]ng).] [L. deprecatus, p. p. of
   deprecari to avert by prayer, to deprecate; de- + precari to
   pray. See Pray.]
   To pray against, as an evil; to seek to avert by prayer; to
   seek deliverance from; to express deep regret for; to desire
   the removal of. [archaic]
   [1913 Webster]

   2. To protest against; to advance reasons against.
      [PJC]

            His purpose was deprecated by all round him, and he
            was with difficulty induced to adandon it. --Sir W.
                                                  Scott.
      [1913 Webster]

   3. To disapprove of strongly; to express a low opinion of.
      [PJC]

WordNet (r) 3.0 (2006):

deprecating
    adj 1: tending to diminish or disparage; "belittling comments";
           "managed a deprecating smile at the compliment";
           "deprecatory remarks about the book"; "a slighting
           remark" [syn: belittling, deprecating, deprecative,
           deprecatory, depreciative, depreciatory,
           slighting]