Impersonator (5)
I believe the answer is:
mimic
'impersonator' is the definition.
(mimic is a kind of impersonator)
This is the entire clue.
(Other definitions for mimic that I've seen before include "Impersonator" , "Impersonate" , "Appear just like" , "Imitate in order to ridicule" , "Imitate for humorous reasons" .)