Leaven (5)
I believe the answer is:
yeast
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">leaven</span>' is the definition.<br/ ><span class="explanation-format__explanation">(yeast is a kind of leaven)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for yeast that I've seen before include "Androgynous" , "Baker's ingredient" , "Leavening agent in bread-making" , "Dough raising agent" , "Rising agent" .)