Be aware of speaker's refusal (4)
I believe the answer is:
know
'be aware of' is the definition.
(thesaurus)
'speaker's refusal' is the wordplay.
'speaker's' shows a homophone (sound like).
'refusal' becomes 'no'.
'no' is a homophone of 'KNOW'.
(Other definitions for know that I've seen before include "Have awareness of" , "Have information" , "Realise" , "Be aware of (something)" , "Articulated" .)