1.  uncommon(a = adj.all) - 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"
Antonym: common
Derived form noun uncommonness₂

2.  uncommon(s = adj.all) rare - marked by an uncommon quality; especially superlative or extreme of its kind; "what is so rare as a day in June"; "a rare skill"; "an uncommon sense of humor"; "she was kind to an uncommon degree"
Derived form noun uncommonness₁

   Not common; unusual; infrequent; rare; hence, remarkable; strange; as, an uncommon season; an uncommon degree of cold or heat; uncommon courage. [1913 Webster]

uncommon, adj. & adv.
--adj.
1 not common; unusual; remarkable.
2 remarkably great etc. (an uncommon fear of spiders).
--adv. archaic uncommonly (he was uncommon fat).

Derivative:
uncommonly adv. uncommonness n.

N  unconformity, nonconformity, unconformity, disconformity, unconventionality, informality, abnormity, abnormality, anomaly, anomalousness, exception, peculiarity, infraction of law, breach, of law, violation of law, violation of custom, violation of usage, infringement of law, infringement of custom, infringement of usage, teratism, eccentricity, bizarrerie, oddity, je ne sais quoi, monster, monstrosity, rarity, freak, freak of Nature, weirdo, mutant, rouser, snorter, individuality, idiosyncrasy, originality, mannerism, aberration, irregularity, variety, singularity, exemption, salvo, nonconformist, nondescript, character, original, nonesuch, nonsuch, monster, prodigy, wonder, miracle, curiosity, flying fish, black sheep, black swan, lusus naturae, rara avis, queer fish, mongrel, random breed, half-caste, half-blood, half-breed, metis, crossbreed, hybrid, mule, hinny, mulatto, tertium quid, hermaphrodite, phoenix, chimera, hydra, sphinx, minotaur, griffin, griffon, centaur, saggittary, kraken, cockatrice, wyvern, roc, dragon, sea serpent, mermaid, merman, merfolk, unicorn, Cyclops, men whose heads do grow beneath their shoulders, teratology, fish out of water, neither one thing nor another, neither fish nor fowl, neither fish flesh nor fowl nor good red herring, one in a million, one in a way, one in a thousand, outcast, outlaw, off the beaten track, oasis, uncomformable, exceptional, abnormal, abnormous, anomalous, anomalistic, out of order, out of place, out of keeping, out of tune, out of one's element, irregular, arbitrary, teratogenic, lawless, informal, aberrant, stray, wandering, wanton, peculiar, exclusive, unnatural, eccentric, egregious, out of the beaten track, off the beaten track, out of the common, out of the common run, beyond the pale of, out of the pale of, misplaced, funny, unusual, unaccustomed, uncustomary, unwonted, uncommon, rare, curious, odd, extraordinary, out of the ordinary, strange, monstrous, wonderful, unexpected, unaccountable, outre, out of the way, remarkable, noteworthy, queer, quaint, nondescript, none such, sui generis, unfashionable, fantastic, grotesque, bizarre, outlandish, exotic, tombe des nues, preternatural, denaturalized, heterogeneous, heteroclite, amorphous, mongrel, amphibious, epicene, half blood, hybrid, androgynous, androgynal, asymmetric, adelomorphous, bisexual, hermaphrodite, monoclinous, qualified, singular, unique, one-of-a-kind, newfangled, novel, non-classical, original, unconventional, unheard of, unfamiliar, undescribed, unprecedented, unparalleled, unexampled, unconformably, except, unless, save barring, beside, without, save and except, let alone, however, yet, but, once in a blue moon, once in a million years, Int, what on earth!, what in the world!, What the devil!, Holy cow!, Can you top that?, Sacre bleu, never was seen the like, never was heard the like, never was known the like, I could hardly believe it, I saw it, but I didn't believe it.