Expert, connoisseur (5)
I believe the answer is:
maven
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">expert</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that maven is a type of expert)</span><br/ ><br/ >'<span class="explanation-format__original">connoisseur</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ ></span>
(Other definitions for maven that I've seen before include "Expert, connoisseur (US)" , "US authority" .)