Accede, acquiesce (6)
I believe the answer is:
assent
I believe this is a double definition.
'accede' is the first definition.
(I know that accede can be written as assent)
'acquiesce' is the second definition.
(I know that acquiesce can be written as assent)
(Other definitions for assent that I've seen before include "Give consent" , "Say yes" , "Consent or approval" , "Accede, acquiesce" , "Express approval or agreement" .)