Disadvantage to lose top copy (9)
I believe the answer is:
imitation
'copy' is the definition.
(imitation is a kind of copy)
'disadvantage to lose top' is the wordplay.
'disadvantage' becomes 'limitation' (limitation is a kind of disadvantage).
'to lose top' means to remove the first letter.
'limitation' with its first letter taken away is 'IMITATION'.
(Other definitions for imitation that I've seen before include "Forgery" , "Artificial" , "Sincerest flattery maybe" , "Act of copying" , "Unoriginal" .)