Deny detective's professional and extremely virile (8)
I believe the answer is:
disprove
'deny' is the definition.
(thesaurus)
'detective's professional and extremely virile' is the wordplay.
'detective's' becomes 'dis' (Detective Inspector).
'professional' becomes 'pro' ('pro' can be a synonym of 'professional').
'and' is a charade indicator (letters next to each other).
'extremely' says to hollow out the word (remove centre letters).
'virile' with its centre taken out is 've'.
'dis'+'pro'+'ve'='DISPROVE'
(Other definitions for disprove that I've seen before include "Show to be false - so provide" , "Demonstrate to be false" , "Refute, rebut" , "Negate" , "challenge successfully?" .)