Cocksure (13)
I believe the answer is:
overconfident
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cocksure</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for overconfident that I've seen before include "Too bold or certain" , "Too bullish" , "Too certain of oneself" , "Cock-sure" , "Too sure of oneself" .)