Absolve former partner - one on charge (9)
I believe the answer is:
exonerate
'absolve' is the definition.
(I've seen this in another clue)
'former partner one on charge' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'on' says to put letters next to each other.
'charge' becomes 'rate' (rate is a kind of charge).
'ex'+'one'+'rate'='EXONERATE'
(Other definitions for exonerate that I've seen before include "Officially absolve from blame" , "Discharge" , "Declare to be free from blame" , "let off the hook" , "Declare to be blameless (9)" .)