Servant is back working in hall (7)
I believe the answer is:
mansion
'hall' is the definition.
('mansion' can be a synonym of 'hall')
'servant is back working' is the wordplay.
'servant' becomes 'man' (man is a kind of servant).
'back' says the letters should be written in reverse.
'working' becomes 'on'.
'is' written backwards gives 'si'.
'man'+'si'+'on'='MANSION'
'in' acts as a link.
(Other definitions for mansion that I've seen before include "Huge imposing residence" , "Large dwelling" , "Stately home" , "Imposing house" , "Impressive house" .)