The Collaborative International Dictionary of English v.0.48:

Sicken \Sick"en\, v. i.
   1. To become sick; to fall into disease.
      [1913 Webster]

            The judges that sat upon the jail, and those that
            attended, sickened upon it and died.  --Bacon.
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   2. To be filled to disgust; to be disgusted or nauseated; to
      be filled with abhorrence or aversion; to be surfeited or
      satiated.
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            Mine eyes did sicken at the sight.    --Shak.
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   3. To become disgusting or tedious.
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            The toiling pleasure sickens into pain. --Goldsmith.
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   4. To become weak; to decay; to languish.
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            All pleasures sicken, and all glories sink. --Pope.
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The Collaborative International Dictionary of English v.0.48:

Sicken \Sick"en\, v. t. [imp. & p. p. Sickened; p. pr. & vb.
   n. Sickening.]
   1. To make sick; to disease.
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            Raise this strength, and sicken that to death.
                                                  --Prior.
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   2. To make qualmish; to nauseate; to disgust; as, to sicken
      the stomach.
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   3. To impair; to weaken. [Obs.] --Shak.
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WordNet (r) 3.0 (2006):

sicken
    v 1: cause aversion in; offend the moral sense of; "The
         pornographic pictures sickened us" [syn: disgust,
         revolt, nauseate, sicken, churn up]
    2: get sick; "She fell sick last Friday, and now she is in the
       hospital" [syn: sicken, come down]
    3: upset and make nauseated; "The smell of the food turned the
       pregnant woman's stomach"; "The mold on the food sickened the
       diners" [syn: sicken, nauseate, turn one's stomach]
    4: make sick or ill; "This kind of food sickens me"