The Collaborative International Dictionary of English v.0.48:

Curious \Cu"ri*ous\ (k?"r?-?s), a. [OF. curios, curius, F.
   curieux, L. curiosus careful, inquisitive, fr. cura care. See
   Cure.]
   1. Difficult to please or satisfy; solicitous to be correct;
      careful; scrupulous; nice; exact. [Obs.]
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            Little curious in her clothes.        --Fuller.
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            How shall we,
            If he be curious, work upon his faith? --Beau. & Fl.
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   2. Exhibiting care or nicety; artfully constructed;
      elaborate; wrought with elegance or skill.
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            To devise curious works.              --Ex. xxxv. 32
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            His body couched in a curious bed.    --Shak.
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   3. Careful or anxious to learn; eager for knowledge; given to
      research or inquiry; habitually inquisitive; prying; --
      sometimes with after or of.
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            It is a pity a gentleman so very curious after
            things that were elegant and beautiful should not
            have been as curious as to their origin, their uses,
            and their natural history.            --Woodward.
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   4. Exciting attention or inquiry; awakening surprise;
      inviting and rewarding inquisitiveness; not simple or
      plain; strange; rare. "Acurious tale" --Shak.
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            A multitude of curious analogies.     --Macaulay.
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            Many a quaint and curious volume of forgotten lore.
                                                  --E. A. Poe.
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            Abstruse investigations in recondite branches of
            learning or sciense often bring to light curious
            results.                              --C. J. Smith.
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   Curious arts, magic. [Obs.]
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            Many . . . which used curious arts brought their
            books together, and burned them.      --Acts xix.
                                                  19.

   Syn: Inquisitive; prying. See Inquisitive.
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WordNet (r) 3.0 (2006):

curious
    adj 1: beyond or deviating from the usual or expected; "a
           curious hybrid accent"; "her speech has a funny twang";
           "they have some funny ideas about war"; "had an odd
           name"; "the peculiar aromatic odor of cloves"; "something
           definitely queer about this town"; "what a rum fellow";
           "singular behavior" [syn: curious, funny, odd,
           peculiar, queer, rum, rummy, singular]
    2: eager to investigate and learn or learn more (sometimes about
       others' concerns); "a curious child is a teacher's delight";
       "a trap door that made me curious"; "curious investigators";
       "traffic was slowed by curious rubberneckers"; "curious about
       the neighbor's doings" [ant: incurious]
    3: having curiosity aroused; eagerly interested in learning
       more; "a trap door that made me curious"

Moby Thesaurus II by Grady Ward, 1.0:

112 Moby Thesaurus words for "curious":
   aberrant, abnormal, absurd, agape, agog, all agog, analytical,
   attentive, attracted, barmy, bizarre, burning with curiosity,
   careful, catechistic, cathectic, cautious, circumspect, concerned,
   considerate, consumed with curiosity, deviant, deviate, eccentric,
   enthusiastic, erratic, examining, excited, exotic, extraordinary,
   fascinated, freaked out, freakish, freaky, funny, ghoulish,
   gossipy, grotesque, heedful, impertinent, inquiring, inquisitional,
   inquisitive, inquisitorial, interested, interfering, intermeddling,
   interrogational, interrogative, interrogatory, intrusive,
   investigative, irregular, itchy, keen on, kinky, kooky, loving,
   meddlesome, meddling, mindful, morbid, morbidly curious, nosy,
   nuts, nutty, odd, oddball, off, off the wall, offbeat, open-eyed,
   openmouthed, out, outlandish, outrageous, outre, overcurious,
   passing strange, passionate, peculiar, piqued, pixilated, prurient,
   prying, quaint, queer, querying, questioning, quizzical, quizzing,
   regardful, scopophiliac, scrutinizing, searching, singular,
   snooping, snoopy, solicitous, strange, supercurious, tantalized,
   tender, thoughtful, tickled, titillated, turned-on, unconventional,
   unearthly, unusual, voyeuristic, weird, wondrous strange