Wow! A man has to speak to verify (11)
I believe the answer is:
corroborate
'to verify' is the definition.
(thesaurus)
'wow a man has to speak' is the wordplay.
'wow' becomes 'cor' (both are expressions of surprise).
'a man' becomes 'rob' ().
'has' says to put letters next to each other.
'to speak' becomes 'orate' (orating is a kind of speaking).
'cor'+'rob'+'orate'='CORROBORATE'
(Other definitions for corroborate that I've seen before include "Confirm - support" , "Confirm (a statement)" , "Back up (a statement)" , "Bear out" .)