Meaning

noun a criminal who illegally sets fire to property

noun a bomb that is designed to start fires; is most effective against flammable targets (such as fuel)

adjective involving deliberate burning of property

originFrom Middle English incendiarie, from Old French incendiaire, from Latin incendiārius (“setting alight”), from incendium (“destructive fire”), from incendō (“to set on fire, kindle”), from in- (“into, in, on, upon”) + candeō (“to be hot”).

Etymology from Wiktionary, CC BY-SA 3.0