Crazy poseur prepared to accept bill (12)
I believe the answer is:
preposterous
'crazy' is the definition.
(I've seen this before)
'poseur prepared to accept bill' is the wordplay.
'prepared' indicates anagramming the letters.
'to accept' is an insertion indicator.
'bill' becomes 'poster' (synonyms).
'poseur' with letters rearranged gives 'preous'.
'preous' going around 'poster' is 'PREPOSTEROUS'.
(Other definitions for preposterous that I've seen before include "Utterly absurd" , "Unreasonable - fatuous" , "Utterly ridiculous" , "Ludicrous" , "Laughable" .)