Policeman promises to pay in full (7)
I believe the answer is:
copious
'full' is the definition.
(I've seen this before)
'policeman promises to pay' is the wordplay.
'policeman' becomes 'cop' (slang term).
'promises to pay' becomes 'IOU's' (promises to pay a debt).
'cop'+'ious'='COPIOUS'
'in' acts as a link.
(Other definitions for copious that I've seen before include "Many" , "abundance" , "Providing loads of" , "great supply?" , "Redundant" .)