"She does it at mealtimes, in the loos, all over the place."
- Hermione, speaking of Cho (OP21)
U.S.: restroom or toilet.
"lavatory," 1940, but perhaps 1922, probably from French lieux d'aisances, "lavatory," literally "place of ease," picked up by British servicemen in France during World War I. Or possibly a pun on Waterloo, based on water closet. (via Online Etymology Dictionary)