'A' f-for agreement (5)
I believe the answer is:
appro
'agreement' is the definition.
(I've seen this before)
'a f-for' is the wordplay.
'f-for' becomes 'p-pro' ('pro' said with a stammer like 'for' was; as in being 'pro' something).
'a'+'ppro'='APPRO'
(Other definitions for appro that I've seen before include "Form of sanction" , "for acceptance, briefly" , "agreement" , "back" , "On which one may examine" .)