Cancel credit in advance (5)
I believe the answer is:
scrub
'cancel' is the definition.
(thesaurus)
'credit in advance' is the wordplay.
'credit' becomes 'cr'.
'in' indicates putting letters inside.
'advance' becomes 'sub' (I've seen this in other clues).
'cr' going inside 'sub' is 'SCRUB'.
(Other definitions for scrub that I've seen before include "Scour; brushwood" , "Get rid of" , "remove cosmetic" , "Clean thoroughly - cancel" , "Powerful wash" .)