Imitate policeman before the Fourth of July (4)
I believe the answer is:
copy
'imitate' is the definition.
(synonyms)
'policeman before the fourth of july' is the wordplay.
'policeman' becomes 'cop' (slang term).
'before' is a charade indicator (letters next to each other).
'the fourth of july' becomes 'y' (fourth letter of the word 'July').
'cop'+'y'='COPY'
(Other definitions for copy that I've seen before include "Ape; replica" , "Imitation or reproduction" , "Replicate" , "Matter to be printed; ape" , "Closely imitate" .)