Cancel credit accepted by reserve (5)
I believe the answer is:
scrub
'cancel' is the definition.
(thesaurus)
'credit accepted by reserve' is the wordplay.
'credit' becomes 'cr'.
'accepted by' indicates putting letters inside.
'reserve' becomes 'sub' (I've seen this in other clues).
'cr' put within 'sub' is 'SCRUB'.
(Other definitions for scrub that I've seen before include "Rub hard to clean" , "Cleanse" , "Take out - clean" , "clean-up" , "Clean vigorously - stunted vegetation" .)