Meaning

noun a town in central Belgium where in 1815 Napoleon met his final defeat

noun a final crushing defeat

noun 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

originFrom Middle Dutch, composed of water (“water”) + loo (“sacred wood, forest”). More at water, lea. cf. German Loh. Most places in English-speaking countries are named for the battle.

Etymology from Wiktionary, CC BY-SA 3.0