Redundant former partner returned gift (5)
I believe the answer is:
extra
'redundant' is the definition.
(synonyms)
'former partner returned gift' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'returned' is a reversal indicator.
'gift' becomes 'art' ().
'art' back-to-front is 'tra'.
'ex'+'tra'='EXTRA'
(Other definitions for extra that I've seen before include "Minor person screened" , "Unnecessary" , "Bonus; supplement" , "on top" , "Bye or wide, for example" .)