Gradient Newton proved (5)
I believe the answer is:
risen
'proved' is the definition.
('rise' can be a synonym of 'prove')
'gradient newton' is the wordplay.
'gradient' becomes 'rise' (rise is a kind of gradient).
'newton' becomes 'N' (symbol for the scientific unit of force).
'rise'+'n'='RISEN'
(Other definitions for risen that I've seen before include "Got up" , "mounted a rebellion" , "Resin (anag.)" , "Ascended - revolted" , "Grown up" .)