Meaning

noun a toilet in Britain

originUncertain, although usually derived in some way from Waterloo, the site of Wellington's 1815 victory over Napoleon, likely via a pun based on water closet. Other suggested derivations include corruptions of French l'eau (“water”), lieu (“place”), lieux d'aisances (“'places of convenience': a lavatory”), lieu à l'anglaise (“'English place': a British-style lavatory”), bordalou (“a diminutive…

Etymology from Wiktionary, CC BY-SA 3.0