A four flush (also flush draw) is a poker draw or non-standard poker hand that is one card short of being a full flush.[1] Four flushing refers to empty boasting[2] or unsuccessful bluffing,[3] and a four flusher is a person who makes empty boasts or bluffs when holding a four flush.[1][4] Four flusher can also refer to a welcher, piker, or braggart.[5] This pejorative term originated in the 19th century when bluffing poker players misrepresented that they had a flush—a poker hand with five cards all of one suit—when they only had four cards of one suit.[3][4][6] Optimal strategies for bluffing or folding when holding a four flush have been explored extensively in poker strategy books.[7][8][9][10][11]
In New York and Vegas, the phrase is "four flusher", to denote a poker player holding a worthless hand, one card shy of a powerful flush, but bluffing in the hope that opponents will mistake his smirk for strength.
But the term is usually applied to one who "bulls" his way through life with a terrific "front" and who when "called," absolutely fails to "deliver the goods."
It seems then, that a "four flusher" properly speaking, must be an unsuccessful bluffer
A four-flusher originally was someone who bluffs or otherwise can't back up his or her bragging
From one of the book's many tables, Optimal Strategy for the Four Flusher, we learn that if you hold four cards to a flush, have called the opening bettor and have failed to make your flush, you should bluff once in every two cases that you can make a bet the size of the pot.