A person who bluffs or engages in trickery; a fake, fraud, or con artist.
From 'four flush' (a worthless poker hand with four cards of one suit), someone who bluffs about having a winning hand; American slang from gambling culture, late 1800s.
In poker, a 'four flush' looks almost like a real 'flush,' so 'four-flusher' perfectly describes someone who fake-pretends to be something they're not—the gambling term became a general insult!
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