Redden (5)
I believe the answer is:
blush
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">redden</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for blush that I've seen before include "Show embarrassment" , "look embarrassed" , "Redden in shame or modesty" , "Colour" , "Turn red, in embarrassment or shame" .)