The Collaborative International Dictionary of English v.0.48:

Detract \De*tract"\, v. i.
   To take away a part or something, especially from one's
   credit; to lessen reputation; to derogate; to defame; --
   often with from.
   [1913 Webster]

         It has been the fashion to detract both from the moral
         and literary character of Cicero.        --V. Knox.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Detract \De*tract"\, v. t. [imp. & p. p. Detracted; p. pr. &
   vb. n. Detracting.] [L. detractus, p. p. of detrahere to
   detract; de + trahere to draw: cf. F. d['e]tracter. See
   Trace.]
   1. To take away; to withdraw.
      [1913 Webster]

            Detract much from the view of the without. --Sir H.
                                                  Wotton.
      [1913 Webster]

   2. To take credit or reputation from; to defame.
      [1913 Webster]

            That calumnious critic . . .
            Detracting what laboriously we do.    --Drayton.

   Syn: To derogate; decry; disparage; depreciate; asperse;
        vilify; defame; traduce. See Decry.
        [1913 Webster]

WordNet (r) 3.0 (2006):

detract
    v 1: take away a part from; diminish; "His bad manners detract
         from his good character" [syn: take away, detract]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "detract":
   abate, abrade, abstract, bate, beguile, call away, curtail,
   decrease, deduct, depreciate, derogate, detract attention,
   detract from, diminish, disparage, distract, divert,
   divert the mind, drain, eat away, erode, extract, file away,
   impair, leach, lessen, purify, reduce, refine, remove, retrench,
   rub away, shorten, subduct, subtract, take away, take away from,
   take from, thin, thin out, wear away, weed, withdraw