Bank subsidy about to expire (8)
I believe the answer is:
gradient
'bank' is the definition.
(both can mean sloped ground)
'subsidy about to expire' is the wordplay.
'subsidy' becomes 'grant' (I've seen this before).
'about' indicates putting letters inside.
'to expire' becomes 'die' (synonyms).
'grant' going around 'die' is 'GRADIENT'.
(Other definitions for gradient that I've seen before include "Third OT book" , "Rise" , "Treading (anag) - slope" , "Measure of slope" , "Angle of slope" .)