Trouble English magistrate (4)
I believe the answer is:
doge
'magistrate' is the definition.
(doge is a kind of magistrate)
'trouble english' is the wordplay.
'trouble' becomes 'dog' (dog can mean to trouble or plague someone).
'english' becomes 'e' (abbreviation).
'dog'+'e'='DOGE'
(Other definitions for doge that I've seen before include "Magistrate of 14 (historical)" , "Venetian leader" , "Old Italian chief magistrate" , "Ancient lord of Venice" , "Old chief magistrate in Venice and Genoa" .)