Incendiary liquid (6)
I believe the answer is:
napalm
'incendiary liquid' is the definition.
(I've seen this before)
This is the entire clue.
(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" .)