Makes pure (7)
I believe the answer is:
refines
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">makes pure</span>' is the definition.<br/ ><span class="explanation-format__explanation">(refining is a kind of making pure)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for refines that I've seen before include "Frees from impurities" , "Makes purer" .)