That’s not the full story, though. As Doug K. mentioned above, as a general term for a hustler, “shark” predates “sharp”, deriving from the German Schorke or Schurke.
So while “card sharp” may predate “card shark”, that’s just because it happened to appear at a time when shark had already been corrupted into sharp. The preferred form switches back and forth depending on the time and place.
In any case, this isn’t a case of a fossil word, like deserts turning into desserts. “Sharp” and “shark” have equal historical legitimacy and at this point are synonyms (though there may be slight differences in connotation). Arguably, they’re just different spellings for the same word.
Yes, that’s what the painting is called today in English, but that doesn’t mean the English term dates to 1594. The artist Caravaggio was Italian, and the Italian title is “I bari” (“the cheaters”). Th English noun sharp (“a cheater”) is from the 1790s, a shortened form of the earlier sharper from the 1680s.
I know both phrases, in my mind a sharp is a cheater in games played for money and a shark is aggressively competitive. However that’s only what I think now after I’ve been made aware of the distinction.
