1530s, "exclusive control of a commodity or trade," from Latin monopolium, from Greek monopōlion "right of exclusive sale," from monos "single, alone" (from PIE root *men- (4) "small, isolated") + pōlein "to sell," from PIE root *pel- (4) "to sell."
Alternative form monopole (1540s, from the Old French form of the word) was common in 16c. Meaning "possession of anything to the exclusion of others" is by 1640s; sense of "a company or corporation which enjoys a monopoly" is by 1871. The popular board game, developed in its final version by Charles Darrow (1889-1967) and marketed by Parker Brothers, is from 1935, the year it was a craze. Monopoly money "unreal currency" is attested by 1959, in reference to the paper used in the game.