Whitener (6)
I believe the answer is:
bleach
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">whitener</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for bleach that I've seen before include "Household cleaner" , "Strong cleaner" , "Get lighter" , "Whitening agent" , "Chemical whitener" .)