The Collaborative International Dictionary of English v.0.48:

Obscene \Ob*scene"\, a. [L. obscenus, obscaenus, obscoenus, ill
   looking, filthy, obscene: cf. F. obsc['e]ne.]
   [1913 Webster]
   1. Offensive to chastity or modesty; expressing or presenting
      to the mind or view something which delicacy, purity, and
      decency forbid to be exposed; impure; as, obscene
      language; obscene pictures.
      [1913 Webster]

            Words that were once chaste, by frequent use grew
            obscene and uncleanly.                --I. Watts.
      [1913 Webster]

   2. Foul; fifthy; disgusting.
      [1913 Webster]

            A girdle foul with grease binds his obscene attire.
                                                  --Dryden
                                                  (Aeneid, vi.
                                                  417).
      [1913 Webster]

   3. Inauspicious; ill-omened. [R.] [A Latinism]
      [1913 Webster]

            At the cheerful light,
            The groaning ghosts and birds obscene take flight.
                                                  --Dryden.
      [1913 Webster]

   Syn: Impure; immodest; indecent; unchaste; lewd.
        [1913 Webster] -- Ob*scene"ly, adv. --
        Ob*scene"ness, n.
        [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

172 Moby Thesaurus words for "obscene":
   Cyprian, Fescennine, Paphian, Rabelaisian, abhorrent, abominable,
   abusive, amoral, animal, aphrodisiomaniacal, atrocious, awful,
   barnyard, base, bawdy, beastly, below contempt, beneath contempt,
   blasphemous, blue, broad, calumniatory, calumnious, carnal,
   clitoromaniacal, coarse, comminatory, concupiscent, contemptible,
   contumelious, crass, crude, crusty, cursing, damnatory, debauched,
   degenerate, denunciatory, despicable, detestable, dirty,
   disgusting, dissolute, distasteful, dysphemistic, earthy,
   epithetic, erotic, eroticomaniacal, erotomaniacal, evil,
   excommunicative, excommunicatory, execrable, execratory, fetid,
   filthy, fleshly, forbidding, foul, foul-mouthed, foul-spoken,
   foul-tongued, foulmouthed, fulminatory, fulsome, gaudy, goatish,
   gross, gynecomaniacal, hateful, heinous, hideous, horny, horrible,
   hot, hysteromaniacal, ignoble, immodest, immoral, imprecatory,
   improper, impure, indecent, indecorous, indelicate, inelegant,
   insufferable, intolerable, ithyphallic, lascivious, lecherous,
   lewd, libertine, libidinous, licentious, lickerish, loathsome,
   loose, loud, lubricious, lurid, lustful, maledictory, malodorous,
   mephitic, meretricious, miasmal, miasmic, nasty, nauseating,
   nauseous, noisome, noxious, nymphomaniacal, objectionable,
   obnoxious, odious, off color, offensive, outrageous, paw,
   pornographic, priapic, profane, prurient, randy, rank, raunchy,
   raw, rebarbative, repellent, repugnant, repulsive, revolting,
   ribald, rich, risque, rocky, rough, rude, ruttish, salacious,
   satyric, scabrous, scatologic, scatological, scurrile, scurrilous,
   sensual, sexual, sexy, shameful, shameless, shocking, sickening,
   smoking-room, smutty, stinking, suggestive, sultry, unchaste,
   unclean, unpalatable, unprintable, unrepeatable, vile,
   vituperative, vulgar, wanton, warm, wicked