Former lover capsizing craft, unusually (5)
I believe the answer is:
extra
'unusually' is the definition.
(I've seen this before)
'former lover capsizing craft' is the wordplay.
'former lover' becomes 'ex'.
'capsizing' says the letters should be written backwards.
'craft' becomes 'art' (I've seen this before).
'art' back-to-front is 'tra'.
'ex'+'tra'='EXTRA'
(Other definitions for extra that I've seen before include "Bit actor in movie's crowd scenes" , "One has no lines" , "Surcharge" , "Surplus to requirements" , "(Theatrical) spear carrier" .)