Incendiary liquid (6)
I believe the answer is:
napalm
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">incendiary liquid</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for napalm that I've seen before include "Petroleum jelly used in bombs and flame-throwers" , "Highly flammable jelly" , "Incendiary jelly used in flamethrowers" , "Liquid used in flame-throwers" , "Incendiary agent" .)