Waterloo (n.)

village near Brussels; the great battle there took place June 18, 1815; extended sense of "a final, crushing defeat" is first attested 1816 in letter of Lord Byron. The second element in the place name is from Flemish loo "sacred wood" (see lea (n.)).

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Definitions of Waterloo from WordNet
waterloo (n.)
a final crushing defeat;
he met his waterloo
Waterloo (n.)
a town in central Belgium where in 1815 Napoleon met his final defeat;
Waterloo (n.)
the battle on 18 June 1815 in which Prussian and British forces under Blucher and the Duke of Wellington routed the French forces under Napoleon;
Synonyms: Battle of Waterloo