Don't take no for an answer (6)
I believe the answer is:
insist
'don't take no for an answer' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for insist that I've seen before include "Be adamant" , "Be firm in demands" , "Continue to assert, maintain" , "Maintain firmly" , "Refuse to give way" .)