The Collaborative International Dictionary of English v.0.48:

Connoisseur \Con`nois*seur"\ (?; 277), n. [F. connaisseur,
   formerly connoisseur, fr. conna[^i]tre to know, fr. L.
   cognoscere to become acquainted with; co- + noscere,
   gnoscere, to learn to know. See Know, and cf. Cognizor.]
   One well versed in any subject; a skillful or knowing person;
   a critical judge of any art, particulary of one of the fine
   arts.
   [1913 Webster]

         The connoisseur is "one who knows," as opposed to the
         dilettant, who only "thinks he knows."   --Fairholt.
   [1913 Webster]

WordNet (r) 3.0 (2006):

connoisseur
    n 1: an expert able to appreciate a field; especially in the
         fine arts [syn: connoisseur, cognoscente]

Moby Thesaurus II by Grady Ward, 1.0:

96 Moby Thesaurus words for "connoisseur":
   Admirable Crichton, accumulator, adept, aesthete, aficionado,
   amateur, annotator, arbiter, arbiter elegantiarum,
   arbiter of taste, artisan, artist, attache, authority,
   bill collector, bon vivant, buff, captious critic, carper, caviler,
   censor, censurer, cognoscente, collection agent, collector,
   commentator, commenter, connaisseur, consultant, cordon bleu,
   crack shot, craftsman, critic, criticaster, criticizer, critickin,
   criticule, dead shot, dilettante, diplomat, diplomatist, douanier,
   dunner, editor, elder statesman, epicure, epicurean, exciseman,
   experienced hand, expert, expert consultant, fan, farmer,
   faultfinder, freak, gatherer, good judge, gourmand, gourmet,
   graduate, handy man, journeyman, judge, literary critic, magpie,
   man of letters, marksman, maven, miser, muckraker, no slouch, nut,
   pack rat, politician, pro, professional, professor, proficient,
   pundit, refined palate, reviewer, savant, scholar, scholiast,
   shark, sharp, smellfungus, social critic, specialist, statesman,
   tax collector, technical adviser, technical expert, technician,
   textual critic, virtuoso



The Devil's Dictionary (1881-1906):

CONNOISSEUR, n.  A specialist who knows everything about something and
nothing about anything else.
    An old wine-bibber having been smashed in a railway collision,
some wine was pouted on his lips to revive him.  "Pauillac, 1873," he
murmured and died.