Undergo combustion (4)
I believe the answer is:
burn
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">undergo combustion</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for burn that I've seen before include "runner?" , "Heat injury; stream" , "Scorch - stream" , "be consumed" , "Cremate" .)