Green’s Dictionary of Slang

three-card monte n.

also three-card mollie, three-card molly
[Sp. monte, a 19C game of chance, played with 45 cards. The modern game is played only by confidence tricksters. There is no gambling and unless the trickster desires otherwise – to entice a new victim – the house invariably wins; however, note Asbury Sucker’s Progress (1938): ‘Three-Card Monte was a Mexican invention, and a misnomer if ever there was one, for it had no more actual relationship to Monte than to Old Maid.’]

1. [late 19C+] (orig. US) the three-card trick.

2. attrib. use of sense 1.

In compounds

three-card charlie (n.)

one who conducts the game.

three-card (monte) man (n.) (also three-card bloke)

one who conducts the game.