Monopoly BrE AmE trademark
a very popular type of ↑ board game that has been sold since the 1930s. Players use toy money to buy streets and buildings on squares on the board, and then make other players pay rent if they move onto those squares. The squares on the board show the names of real streets in cities in the US (=in an American Monopoly set), London (=in a British Monopoly set), or other big cities around the world. People sometimes use the expression Monopoly money to mean a very large amount of money:
You know how much it costs to buy an apartment in Tokyo? It's Monopoly money!