A card sharp (also cardsharp, card shark or cardshark, sometimes hyphenated) is a person who uses skill and/or deception to win at poker or other card games. “Sharp” and “shark” spellings have varied over time and by region.
The label is not always intended as pejorative, and is sometimes used to refer to practitioners of card tricks for entertainment purposes. In general usage, principally in American English and more commonly with the “shark” spelling, the term has also taken on the meaning of an expert card gambler who takes advantage of less-skilled players, also called an advantage player, without any implication of actual cheating at cards, in much the same way that “pool shark” or “pool hustler” can (especially when used by non-players) be intended to refer to a skilled player rather than a cheater or swindler.
A card sharp or shark (by either of the gambling-related definitions) may be a “rounder” who travels, seeking out high-stakes games in which to gamble.
According to the prevailing etymological theory, the term “shark”, originally meaning “parasite” or “one who preys upon others”(cf. loan shark), derives from German Schorke or Schurke (‘rogue’ or ‘rascal’), as did the English word “shirk”. “Sharp” developed in the 17th century from this meaning of “shark” (as apparently did the use of “shark” as a name for the fish), but the phrase “card sharp” predates the variant “card shark”.The original connotation was negative, meaning “swindler” or “cheat”, regardless of spelling, with the more positive connotations of “expert” or “skilled player” arising later, and not supplanting the negative ones.”Card sharp” and “card shark” are synonymous,although American English is somewhat, but informally, beginning to favor “shark” as a positive term versus “sharp” as a negative one.(However, not all American dictionaries agree with this,and some suggest the opposite.)
Phrasefinder puts “card sharp” (or “-sharper”) as the slightly earlier usage, with an 1859 citation for “card-sharper” and “card-sharp” in both Britain and in the US, while “card-shark” is cited to 1893 in the US.