loo [E20] The upper-class author Nancy Mitford introduced the word loo, meaning ‘lavatory’, to many people in print in her 1940 novel Pigeon Pie, but James Joyce used it before her and there is evidence suggesting it was in use before the 20th century. People have put forward different theories many about its origin, but none is conclusive. Perhaps the most plausible suggests the source as Waterloo, a trade name for iron cisterns in the early 20th century. A popular but unlikely one, not least because of their relative dates, refers it to gardyloo, a cry used in 18th-century Edinburgh to warn passers-by that someone was about to throw slops out of a window into the street. It is based on pseudo-French gar de l’eau ‘mind the water’ (real French would be gare l’eau). Another French phrase is behind a third suggestion, that British servicemen in France during the First World War picked up lieux d’aisances ‘places of ease’, used for ‘a lavatory’, and there is some evidence that the French lieux was being used for a lavatory in the late 18th century.