Excessive zeal (10)
I believe the answer is:
fanaticism
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">excessive zeal</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 fanaticism that I've seen before include "Zealotry" , "Excessive zeal" .)