Top archbishop, extremely sexy when defrocked (4)
I believe the answer is:
apex
'top' is the definition.
(apex is a top or peak)
'archbishop extremely sexy when defrocked' is the wordplay.
'extremely' means to remove the middle letters (only the extremes of the word are used).
'when defrocked' means to look at the middle letters (the word\'s covering or \'frock\' is removed).
'archbishop' with its centre taken out is 'ap'.
The middle of 'sexy' is 'ex'.
'ap'+'ex'='APEX'
(Other definitions for apex that I've seen before include "The highest point of something" , "Topmost point" , "Summit - pinnacle" , "reasonable fare" , "Summit or peak" .)