Burn fiercely (5)
I believe the answer is:
blaze
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">burn fiercely</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for blaze that I've seen before include "Fire -- stripe on a horse's head" , "Sensationally announce" , "brilliant" , "glare" , "rage" .)