Superfluous that former skill returned (5)
I believe the answer is:
extra
'superfluous' is the definition.
('extra' can be a synonym of 'superfluous')
'former skill returned' is the wordplay.
'former' becomes 'ex'.
'skill' becomes 'art' (I've seen this before).
'returned' is a reversal indicator.
'art' written backwards gives 'tra'.
'ex'+'tra'='EXTRA'
'that' acts as a link.
(Other definitions for extra that I've seen before include "I may carry spear" , "Studio crowd player" , "Supplemental" , "Another" , "Accessory" .)