The Collaborative International Dictionary of English v.0.48:

Unclean \Un*clean"\ ([u^]n*kl[=e]n"), a. [AS. uncl[=ae]ne. See
   Unnot, and Clean.]
   1. Not clean; foul; dirty; filthy.
      [1913 Webster]

   2. Ceremonially impure; needing ritual cleansing.
      [1913 Webster]

            He that toucheth the dead body of any man shall be
            unclean seven days.                   --Num. xix.
                                                  11.
      [1913 Webster]

   3. Morally impure. "Adultery of the heart, consisting of
      inordinate and unclean affections." --Perkins.
      [1913 Webster] -- Un*clean"ly, adv. -- Un*clean"ness,
      n.
      [1913 Webster]

   Unclean animals (Script.), those which the Israelites were
      forbidden to use for food.

   Unclean spirit (Script.), a wicked spirit; a demon. --Mark
      i. 27.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

146 Moby Thesaurus words for "unclean":
   Adamic, Fescennine, Rabelaisian, abominable, arrant, atrocious,
   awful, backsliding, base, bawdy, beastly, beneath contempt,
   besmirched, black, blameworthy, blue, brutal, carnal, common,
   contaminated, contemptible, corrupted, defiled, deplorable,
   despicable, detestable, dire, dirty, disgusting, dreadful,
   egregious, enormous, erring, fallen, fetid, filthy, flagrant,
   fleshly, foul, foul-mouthed, foul-spoken, foul-tongued, frail,
   fulsome, grievous, gross, grubby, hateful, heinous, horrible,
   horrid, immoral, impure, indecent, infamous, infected, infirm,
   ithyphallic, lamentable, lapsed, lewd, loathsome, lousy, lurid,
   maculate, monstrous, nasty, nefarious, noisome, nonkosher,
   notorious, obnoxious, obscene, odious, of easy virtue, offensive,
   outrageous, peccable, pitiable, pitiful, polluted, pornographic,
   postlapsarian, prodigal, rank, raunchy, recidivist, recidivistic,
   regrettable, reprehensible, repulsive, ribald, ritually unclean,
   rotten, sad, salacious, scandalous, schlock, scurrile, scurrilous,
   scurvy, shabby, shameful, shocking, shoddy, smirched, smoking-room,
   smutty, soiled, soily, sordid, squalid, sullied, sultry, tainted,
   terrible, too bad, tref, unangelic, unbathed, unchaste, uncleanly,
   ungodly, ungood, unprintable, unpure, unrepeatable, unrighteous,
   unsaintly, unscoured, unscrubbed, unswept, unvirginal, unvirtuous,
   unwashed, unwiped, vile, villainous, virtueless, wanton, wayward,
   weak, woeful, worst, worthless, wretched