Throne (3)
'throne' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for seat that I've seen before include "Constituency; location" , "Place to sit" , "Take one and sit" , "Chair, bench, or stool, say" , "Box ---, position of advantage" .)
'throne' is the definition.
(both can informally mean toilet)
This is the entire clue.
(Other definitions for lav that I've seen before include "Loo" , "Private place in short" , "toilet" .)