Bountiful police officer promises to pay (7)
I believe the answer is:
copious
'bountiful' is the definition.
(thesaurus)
'police officer promises to pay' is the wordplay.
'police officer' becomes 'cop' (cop is a kind of police officer).
'promises to pay' becomes 'IOU's' (promises to pay a debt).
'cop'+'ious'='COPIOUS'
(Other definitions for copious that I've seen before include "Abundant in quantity" , "Ample" , "Many" , "full" , "Large in number or quantity" .)