Spare former partner with single charge (9)
I believe the answer is:
exonerate
'spare' is the definition.
(thesaurus)
'former partner with single charge' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'with' is a charade indicator (letters next to each other).
'single' becomes 'one' (a single thing - only one).
'charge' becomes 'rate' (rate is a kind of charge).
'ex'+'one'+'rate'='EXONERATE'
(Other definitions for exonerate that I've seen before include "free of charge" , "Officially absolve from blame" , "Free of duty" , "Discharge" , "Declare to be free from blame" .)