A bill for the magistrate (4)
I believe the answer is:
beak
I believe this clue is a double definition.
'a bill' is the first definition.
(I know that bill can be written as beak)
'the magistrate' is the second definition.
(informal term)
'for' acts as a link.
(Other definitions for beak that I've seen before include "Bill; nose" , "Schoolmarm" , "Horny mouth of a bird" , "Mandible" , "Magistrate -- schoolmaster (old slang)" .)