Grant immunity to former partner, mostly unoccupied (6)
I believe the answer is:
exempt
'grant immunity to' is the definition.
(I've seen this before)
'former partner mostly unoccupied' is the wordplay.
'former partner' becomes 'ex'.
'mostly' means to remove the last letter.
'unoccupied' becomes 'empty' ('empty' can be similar in meaning to 'unoccupied').
'empty' with its final letter removed is 'empt'.
'ex'+'empt'='EXEMPT'
(Other definitions for exempt that I've seen before include "Privileged" , "Not subject to, taxation say" , "Duty-free" , "may mean the taxman may ignore some charge" , "Grant immunity" .)