Waterloo UK /ˌwɔːtəˈluː/US /ˌwɔtɚˈluː/ noun1 •Often in the term meet one's Waterloo: a notable and decisive defeat following an encounter with a powerful opponent or a problem that is too difficult.He flung his dime at a newsboy, got his Express, propped his back against the truck, and was at once rapt in the account of his Waterloo as expanded by the ingenious press. — 1903 formsWaterloos