Refuse to take "no" for an answer (6)
I believe the answer is:
insist
'refuse to take no for an answer' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for insist that I've seen before include "Be firmly demanding" , "Press" , "Refuse to give way" , "Take no refusal" , "Continue to assert, maintain" .)