/ luː; NAmE / noun
( pl. loos ) ( BrE , informal ) a toilet / bathroom :
She's gone to the loo.
Can I use your loo, please?
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WORD ORIGIN
1940s: many theories have been put forward about the word's origin: one suggests the source is Waterloo , a trade name for iron cisterns in the early part of the century; the evidence remains inconclusive.