Copy a key for a girl (5)
I believe the answer is:
mimic
'copy' is the definition.
(mimicking is a kind of copying)
'a key for a girl' is the wordplay.
'a key' becomes 'c' (I've seen this in other clues).
'for' says to put letters next to each other (I've seen this in other clues).
'a girl' becomes 'mimi' (**).
'c' after 'mimi' is 'MIMIC'.
(Other definitions for mimic that I've seen before include "Ape" , "'Copy, imitate (5)'" , "Imitate for humorous reasons" , "Impersonate" , "Imitate in order to ridicule" .)