Nosy magistrate? (4)
I believe the answer is:
'magistrate?' is the definition.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for beak that I've seen before include "Bird's bill" , "Bird bill; magistrate" , "Magistrate -- schoolmaster (old slang)" , "Bill; nose" , "Mandible" .)