The Collaborative International Dictionary of English v.0.48:

Ill \Ill\ ([i^]l), a. [The regular comparative and superlative
   are wanting, their places being supplied by worseand worst,
   from another root.] [OE. ill, ille, Icel. illr; akin to Sw.
   illa, adv., Dan. ilde, adv.]
   1. Contrary to good, in a physical sense; contrary or opposed
      to advantage, happiness, etc.; bad; evil; unfortunate;
      disagreeable; unfavorable.
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            Neither is it ill air only that maketh an ill seat,
            but ill ways, ill markets, and ill neighbors.
                                                  --Bacon.
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            There 's some ill planet reigns.      --Shak.
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   2. Contrary to good, in a moral sense; evil; wicked; wrong;
      iniquitious; naughtly; bad; improper.
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            Of his own body he was ill, and gave
            The clergy ill example.               --Shak.
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   3. Sick; indisposed; unwell; diseased; disordered; as, ill of
      a fever.
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            I am in health, I breathe, and see thee ill. --Shak.
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   4. Not according with rule, fitness, or propriety; incorrect;
      rude; unpolished; inelegant.
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            That 's an ill phrase.                --Shak.
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   Ill at ease, uneasy; uncomfortable; anxious. "I am very ill
      at ease." --Shak.

   Ill blood, enmity; resentment; bad blood.

   Ill breeding, lack of good breeding; rudeness.

   Ill fame, ill or bad repute; as, a house of ill fame, a
      house where lewd persons meet for illicit intercourse.

   Ill humor, a disagreeable mood; bad temper.

   Ill nature, bad disposition or temperament; sullenness;
      esp., a disposition to cause unhappiness to others.

   Ill temper, anger; moroseness; crossness.

   Ill turn.
      (a) An unkind act.
      (b) A slight attack of illness. [Colloq. U.S.] -- Ill
   will, unkindness; enmity; malevolence.

   Syn: Bad; evil; wrong; wicked; sick; unwell.
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WordNet (r) 3.0 (2006):

ill turn
    n 1: an act intended to help that turns out badly; "he did them
         a disservice" [syn: disservice, ill service, ill
         turn] [ant: service]