W.C. (3)
'wc' is the definition.
(both can mean a toilet)
This is the entire clue.
(Other definitions for loo that I've seen before include "Lavatory - old card game" , "Privy" , "WC - old card game" , "In which one goes" , "A colloquial toilet" .)
(Other definitions for lav that I've seen before include "toilet" , "Private place in short" , "Loo" .)
(Other definitions for toilet that I've seen before include "It means washing" , "Plumbing fixture" , "something to go on?" , "Waste disposal unit" , "Smallest room" .)