Connoisseur
Connoisseur (?; 277) , noun
[French connaisseur, formerly connoisseur, from connaître to know, from Latin cognoscere to become acquainted with; co- + noscere, gnoscere, to learn to know. See Know, and compare Cognizor.]
One well versed in any subject; a skillful or knowing person; a critical judge of any art, particularly of one of the fine arts.
The connoisseur is “one who knows,” as opposed to the dilettant, who only “thinks he knows.”