c. 1300, "a wedge, a wedge-shaped piece used for some purpose," from Old French coing (12c.) "a wedge; stamp; piece of money;" usually "corner, angle," from Latin cuneus "a wedge," which is of unknown origin.
The die for stamping metal was wedge-shaped, and by late 14c. the English word came to mean "thing stamped, piece of metal converted into money by being impressed with official marks or characters" (a sense that already had developed in Old French). Meaning "coined money collectively, specie" is from late 14c.
Compare quoin, which split off from this word 16c., taking the architectural sense. Modern French coin is "corner, angle, nook."
The custom of striking coins as money began in western Asia Minor in 7c. B.C.E.; Greek tradition and Herodotus credit the Lydians with being first to make and use coins of silver and gold. Coin-operated (adj.), of machinery, is attested from 1890. Coin collector is attested from 1795.