Additional art picked up after former partner (5)
I believe the answer is:
extra
'additional' is the definition.
(extra means additional or surplus)
'art picked up after former partner' is the wordplay.
'picked up' says the letters should be written in reverse.
'after' means one lot of letters go next to another.
'former partner' becomes 'ex' (an ex-partner).
'art' reversed gives 'tra'.
'tra' put after 'ex' is 'EXTRA'.
(Other definitions for extra that I've seen before include "There's more" , "redundant > spear-carrier" , "Run scored but not off the bat" , "Crowd-scene actor" , "Minor player in film" .)