Saltpetre (5)
I believe the answer is:
nitre
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">saltpetre</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for nitre that I've seen before include "constituent of gunpowder" , "Also known as salt-petre" , "explosive producer?" , "Inert kind of saltpetre" , "Chemical" .)