1. A person who commits arson; arsonist
2. An incendiary agent (as a bomb)
3. A person who excites factions, quarrels, or sedition; agitator

ETYM Latin incendiarius, from incendium a fire, conflagration: cf. French incendiaire. Related to Incense to inflame.
> 1. Arousing to action or rebellion; SYN. incitive, inflammatory, instigative, rabble-rousing, seditious.
2. Capable of catching fire spontaneously or causing fires or burning readily.
3. Involving deliberate burning of property.