Rise in agreement, you say? (6)
I believe the answer is:
ascent
'rise' is the definition.
('ascent' can be a synonym of 'rise')
'agreement you say?' is the wordplay.
'agreement' becomes 'assent' (assent is a kind of agreement).
'you say?' shows a homophone (sound like).
'assent' is a homophone of 'ASCENT'.
'in' is the link.
(Other definitions for ascent that I've seen before include "A rise in status; climb" , "Acclivity" , "made by Hilary and Tenzing" , "progress" , "Upward slope" .)