Consent (to) (5)
'consent to' is the definition.
(agreeing is a kind of consenting to)
This is the entire clue.
(Other definitions for agree that I've seen before include "'Birds in their little nest . . . . .'" , "Go well together" , "Enjoy view in common" , "Square" , "Say yes to a suggestion" .)
(Other definitions for accede that I've seen before include "Agree or enter into office" , "Agree to what is proposed" , "Consent - agree" , "Grant, agree to proposal" , "Assent (to something)" .)