Officer in place -- occupier (10)
I believe the answer is:
lieutenant
'officer' is the definition.
(lieutenant is a kind of officer)
'place occupier' is the wordplay.
'place' becomes 'lieu' ('lieu' can be a synonym of 'place').
'occupier' becomes 'tenant' (tenant is a kind of occupier**).
'lieu'+'tenant'='LIEUTENANT'
'in' acts as a link.
(Other definitions for lieutenant that I've seen before include "Military rank" , "Commissioned officer" , "Deputy" , "Assistant" , "Army rank" .)