Brighten (5)
I believe the answer is:
cheer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">brighten</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for cheer that I've seen before include "Shout encouragingly" , "Buck up" , "Applaud and acclaim" , "party refreshment?" , "one in three, perhaps" .)