Radical; furthest (7)
I believe the answer is:
extreme
This clue is a double definition.
'radical' is the first definition.
(radical can mean revolutionary or extreme)
'furthest' is the second definition.
(synonyms)
(Other definitions for extreme that I've seen before include "Immoderate" , "Furthest or highest degree of something" , "Point furthest away" , "furthest from the centre" , "Most distant" .)