The Collaborative International Dictionary of English v.0.48:

Abhorrent \Ab*hor"rent\, a. [L. abhorens, -rentis, p. pr. of
   abhorrere.]
   1. Abhorring; detesting; having or showing abhorrence;
      loathing; hence, strongly opposed to; as, abhorrent
      thoughts.
      [1913 Webster]

            The persons most abhorrent from blood and treason.
                                                  --Burke.
      [1913 Webster]

            The arts of pleasure in despotic courts
            I spurn abhorrent.                    --Clover.
      [1913 Webster]

   2. Contrary or repugnant; discordant; inconsistent; --
      followed by to. "Injudicious profanation, so abhorrent to
      our stricter principles." --Gibbon.
      [1913 Webster]

   3. Detestable. "Pride, abhorrent as it is." --I. Taylor.
      [1913 Webster]

WordNet (r) 3.0 (2006):

abhorrent
    adj 1: offensive to the mind; "an abhorrent deed"; "the obscene
           massacre at Wounded Knee"; "morally repugnant customs";
           "repulsive behavior"; "the most repulsive character in
           recent novels" [syn: abhorrent, detestable,
           obscene, repugnant, repulsive]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "abhorrent":
   abominable, antipathetic, averse to, base, beastly, below contempt,
   beneath contempt, contemptible, crude, despicable, detestable,
   disgusted, disgusting, dislikable, displeasing, distasteful,
   execrable, fetid, forbidding, foul, fulsome, gross, hateful,
   hating, heinous, horrid, ignoble, intolerable, invidious, loathing,
   loathsome, malodorous, mephitic, miasmal, miasmic, mislikable,
   nasty, nauseating, noisome, noxious, objectionable, obnoxious,
   obscene, odious, offensive, rebarbative, repellent, repugnant,
   repulsive, revolting, revulsive, sickening, stinking, uncongenial,
   uninviting, unlikable, unlovable, unpleasant, unsympathetic,
   vile