Top chap expected? Not entirely (4)

I believe the answer is:

apex

'top' is the definition.
(thesaurus)

'chap expected? not entirely' is the wordplay.
'not entirely' says the answer is hidden in the clue.
'APEX' is hidden within 'chap expected'.

(Other definitions for apex that I've seen before include "Culmination" , "crown" , "Point or summit" , "Top point" , "white collar union" .)

I've seen this clue in The Telegraph.

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