[1] : The Collaborative International Dictionary of English v.0.48

uncommon \uncom"mon\, a.
   not common; unusual; infrequent; rare; hence, remarkable;
   strange; as, an uncommon season; an uncommon degree of cold
   or heat; uncommon courage.
   1913 webster

   syn: rare; scarce; infrequent; unwonted.
        1913 webster -- uncom"monly, adv. --
        uncom"monness, n.
        1913 webster
see also:
uncom"monly uncom"monness 

[2] : WordNet (r) 2.0

uncommon
     adj 1: not common or ordinarily encountered; unusually great in
            amount or remarkable in character or kind; "uncommon
            birds"; "frost and floods are uncommon during these
            months"; "doing an uncommon amount of business"; "an
            uncommon liking for money"; "he owed his greatest debt
            to his mother's uncommon character and ability" ant:
            common
     2: marked by an uncommon quality; especially superlative or
        extreme of its kind; "what is so rare as a day in
        june"-j.r.lowell; "a rare skill"; "an uncommon sense of
        humor"; "she was kind to an uncommon degree" syn: rare
see also:
common rare 

[3] : Moby Thesaurus II by Grady Ward, 1.0

66 moby thesaurus words for "uncommon":
   almost unheard-of, appalling, astonishing, at a premium, breakaway,
   conspicuous, different, egregious, exceptional, extraordinary,
   extremely, fabulous, fantastic, few, formidable, in short supply,
   incredible, infrequent, marked, marvelous, notable, noteworthy,
   noticeable, novel, occasional, of mark, offbeat, original,
   out of print, out of season, out of stock, outstanding, rare,
   rarely, recherche, remarkable, scanty, scarce, seldom,
   seldom met with, seldom seen, signal, singular, slow, sparse,
   sporadic, strange, striking, sui generis, superior, uncommonly,
   uncustomary, undreamed-of, unexpected, unfamiliar, unfrequent,
   unheard-of, unimaginable, unique, unordinary, unthinkable,
   unthought-of, unusual, unusually, unwonted, wonderful

Uncommon >> U Words
Uncommon, definition of term: Uncommon
uncommon_pag1.html