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.
      [1913 Webster]

            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"

Moby Thesaurus II by Grady Ward, 1.0:

69 Moby Thesaurus words for "sicken":
   OD, affect, afflict, appall, be brought down, be felled,
   be struck down, be traumatized, break out, catch, catch cold,
   collapse, come down with, contract, debilitate, degenerate,
   derange, deteriorate, devitalize, disable, disgust, disimprove,
   disorder, enervate, enfeeble, erupt, fail, fall back, fever, get,
   get worse, give offense, go into shock, gross out, grow worse,
   horrify, hospitalize, incapacitate, indispose, invalid, lay up,
   let down, nauseate, offend, overdose, put off, put out, reduce,
   regress, relapse, reluct, repel, repulse, retrograde, retrogress,
   revolt, run a temperature, shock, slacken, slip back, take,
   take ill, turn, turn the stomach, unhinge, unsettle, upset, weaken,
   worsen