Revolutionary, drastic (7)
I believe the answer is:
radical
I believe this is a double definition.
'revolutionary' is the first definition.
(radical can mean revolutionary or extreme)
'drastic' is the second definition.
(I've seen this before)
(Other definitions for radical that I've seen before include "Going to the roots, fundamental as change may be" , "One seeking root and branch reform" , "leftist?" , "(One) favouring fundamental changes" , "Fundamental - thoroughgoing" .)