Potassium nitrate (9)
I believe the answer is:
saltpetre
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">potassium nitrate</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that potassium nitrate can be written as saltpetre)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for saltpetre that I've seen before include "Gunpowder ingredient" , "Nitre" , "explosive component" , "Component of gunpowder" , "It's used as a fertilizer and explosive" .)