British lav (3)
I believe the answer is:
loo
'british lav' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for loo that I've seen before include "Card game; the 'smallest room'" , "Card-game" , "Lavatory - old card game" , "Little boys' room" , "Ladies, perhaps" .)