Jack gets to mimic trick (4)
I believe the answer is:
jape
'trick' is the definition.
(I've seen this before)
'jack gets to mimic' is the wordplay.
'jack' becomes 'j' (playing card abbreviation).
'gets' says to put letters next to each other.
'to mimic' becomes 'ape' (I've seen this before).
'j'+'ape'='JAPE'
(Other definitions for jape that I've seen before include "Practical joke, jest" , "Kid" , "Trick - joke - jest" , "Lark" , "Trick or prank" .)