Lav in a pub (3)
I believe the answer is:
loo
'lav in a pub' 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" , "Toilet (informal)" , "In which one goes" , "A colloquial toilet" , "Little boys' room" .)