a person who is especially competent to pass critical judgments in an art, particularly one of the fine arts, or in matters of taste: a connoisseur of modern art.
2.
a discerning judge of the best in any field: a connoisseur of horses.
1714, from Fr., from O.Fr. conoisseor "a judge, one well-versed," from conoistre, from L. cognoscere "to know," from com- "with" + gnoscere "recognize" (see notice).