Fervent partisan (6)
I believe the answer is:
zealot
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fervent partisan</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for zealot that I've seen before include "Fanatic or extreme enthusiast" , "Fanatic, usually religious" , "Fervent, even militant, proponent of something" , "Fanatic, fiery follower" , "One ardent for cause" .)