Connoisseur, n.
Etymology: [F. connaisseur, formerly connoisseur, fr. connaître to know, fr. L. cognoscere to become acquainted with; co- + noscere, gnoscere, to learn to know. See Know, amd 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. The connoisseur is "one who knows," as opposed to the dilettant, who only "thinks he knows." Fairholt.
Shades of meaning
Fernald has no entry of its own for connoisseur; he lists it under amateur.
Where he writes about it:
Etymologically, the amateur is one who loves, the connoisseur one who knows. — from amateur
A connoisseur is supposed to be so thoroughly informed regarding any art or work as to be able to criticize or select intelligently and authoritatively; there are many incompetent critics, but there can not, in the true sense, be an incompetent connoisseur. — from amateur
The amateur practises to some extent that in regard to which he may not be well informed; the connoisseur is well informed in regard to that which he may not practise at all. — from amateur
Antonyms
none given