Crossword Genius

Top copy, ten required (4)

Ross

I believe the answer is:

apex

'top' is the definition.
(thesaurus)

'copy ten required' is the wordplay.
'copy' becomes 'ape' ('ape' can be a synonym of 'copy').
'ten' becomes 'x' (roman numeral).
'required' says to put letters next to each other.
'ape'+'x'='APEX'

(Other definitions for apex that I've seen before include "Uppermost tip" , "Uppermost point" , "Acme" , "Tip -- top" , "Summit - pinnacle" .)

I've seen this clue in The Telegraph.
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