Copy Ten in the top (4)
I believe the answer is:
apex
'the top' is the definition.
(apex is a top or peak)
'copy ten' is the wordplay.
'copy' becomes 'ape' (ape can mean to copy or imitate).
'ten' becomes 'X' (Roman numeral).
'ape'+'x'='APEX'
'in' acts as a link.
(Other definitions for apex that I've seen before include "Top point" , "Top, highest part" , "climax" , "The highest point or pointed end" , "Apogee, summit" .)