The Collaborative International Dictionary of English v.0.48:

Suspicious \Sus*pi"cious\, a. [OE. suspecious; cf. L.
   suspiciosus. See Suspicion.]
   1. Inclined to suspect; given or prone to suspicion; apt to
      imagine without proof.
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            Nature itself, after it has done an injury, will
            ever be suspicious; and no man can love the person
            he suspects.                          --South.
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            Many mischievous insects are daily at work to make
            men of merit suspicious of each other. --Pope.
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   2. Indicating suspicion, mistrust, or fear.
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            We have a suspicious, fearful, constrained
            countenance.                          --Swift.
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   3. Liable to suspicion; adapted to raise suspicion; giving
      reason to imagine ill; questionable; as, an author of
      suspicious innovations; suspicious circumstances.
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            I spy a black, suspicious, threatening could.
                                                  --Shak.
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   Syn: Jealous; distrustful; mistrustful; doubtful;
        questionable. See Jealous.
        [1913 Webster] -- Sus*pi"cious*ly, adv. --
        Sus*pi"cious*ness, n.
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WordNet (r) 3.0 (2006):

suspicious
    adj 1: openly distrustful and unwilling to confide [syn:
           leery, mistrustful, suspicious, untrusting,
           wary]
    2: not as expected; "there was something fishy about the
       accident"; "up to some funny business"; "some definitely
       queer goings-on"; "a shady deal"; "her motives were suspect";
       "suspicious behavior" [syn: fishy, funny, shady,
       suspect, suspicious]