Reactionary (7)
I believe the answer is:
diehard
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">reactionary</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for diehard that I've seen before include "One to resist change" , "One strongly opposed to change" , "Person who resists change" , "One who won't accept novelty" , "traditionalist" .)