(noun) A person who commits arson or a substance used to start fires; a person who excites factions and quarrels
1. June watched as the incendiary poured kerosene, lit a match, and burned down the banana stand.
2. June pulled the pin from the hand grenade and launched the incendiary into the enemy’s fort.
3. Soon after meeting her sister in law, June realized the girl was an incendiary, causing family feuds and hostile friendships.