Overzealous (5)
I believe the answer is:
rabid
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">overzealous</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for rabid that I've seen before include "Violent; hydrophobic" , "Burning" , "Ill from a mad dog bite?" , "Extreme, fanatical" , "Extremely fanatical" .)