the.com/loo

means A British word for the toilet, used when you want to ask for the bathroom without actually saying 'toilet' or 'bathroom.'

from Genuinely murky — one of etymology's great unsolved cases. Guesses include a corruption of the French 'l'eau' (water), a nod to 'Waterloo' (there was once a brand of chamber pots or a joke along these lines), or a descendant of 'gardyloo,' a cry shouted in old Edinburgh when people tossed slops out of windows into the street, itself from French 'gare de l'eau' ('watch out for the water'). No version is proven. The word surfaces in writing only in the 20th century, leaving its deeper past genuinely unknown.