Radical; furthest (7)
I believe the answer is:
extreme
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">radical</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(radical can mean revolutionary or extreme)</span><br/ ><br/ >'<span class="explanation-format__original">furthest</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(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" .)