Cause to burn (6)
I believe the answer is:
ignite
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cause to burn</span>' is the definition.<br/ ><span class="explanation-format__explanation">(igniting is a kind of causing to burn)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ignite that I've seen before include "Catch fire; provoke" , "Set fire to, light up" , "Kindle Fire" , "Put a match to" , "'Set alight, fire up (6)'" .)