You’re in Vegas, putting your poker skills to the test. As you are raking in the chips from a particularly clever hand, the player to your right smiles broadly and calls you a “card shark.” The one on your left scowls and calls you one, too.

You’re not sure what to do. Is that a compliment? An insult? So you whip out your handy Webster’s New World College Dictionary. The fourth edition, of course. (What? You don’t carry your dictionary to Vegas? Shame on you!)

And you breathe a sigh of relief. A “card shark” is “an expert card player.” The scowler must just be a sore loser. Or maybe he didn’t have his dictionary handy.

But then your eye is caught by the second definition of “card shark”: “cardsharp.” And you blanch at that definition: “cardsharp: a professional cheater at cards.”

You must have misheard one of them: The guy with the smile was congratulating you on your skill, calling you a “card shark”; the guy with the scowl called you a “cardsharp,” and was accusing you of cheating.

But who could differentiate an “k” from a “p“ in the middle of a Vegas casino? And in what world are a compliment and insult differentiated by a single letter, one that could easily be misheard as the other?

Why, in the world of English, of course.

As a result, it’s no wonder that many people don’t know that there even are two separate words, much less two separate words with virtually opposite meanings.

Though Garner’s Modern American Usage says that the misuse of “card shark” for “cardsharp” is at the very early stages, anecdotal evidence based on a Nexis search and personal experience seems to indicate that the two terms are often used interchangeably, if not incorrectly.

For every news article that uses the correct term—one recently called the Italian prime minister a “‘cardsharp’ who cheats and changes the cards of the game”—it’s easy to find one that does not, like the article discussing the magician who had “put many hours into studying the work of fraudulent mediums and psychics along with card sharks and other hustlers.”

It doesn’t help that “cardsharp” is often spelled “card sharp.” Or that the “shark” image is so negative that many might associate the insult with “card shark.” Or that someone would assume that someone who was “sharp” with cards was very good, not deceptive. Nor does it help that many people assume they are the same thing, or that some dictionaries say so, too.

While Wikipedia is far from the first place this column would trust for research, there is an interesting entry discussing the matter, illustrated with paintings by close contemporaries Caravaggio (“The Cardsharps”) and Gerard van Honthorst (“The Cardsharks”). If you can figure out which one shows the cheater, you should take the pot.

As for how the rest of us should deal with it, perhaps the safest course is to just say what you mean: “Nicely played,” or “Cheater!”

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Merrill Perlman managed copy desks across the newsroom at The New York Times, where she worked for 25 years. Follow her on Twitter at @meperl.