Product of combustion (5)
I believe the answer is:
smoke
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">product of combustion</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for smoke that I've seen before include "Visible vapour" , "'There's no . . . . . without fire'" , "cause of a cough?" , "Use tobacco" , "Cure (eg, herring)" .)