1. arsonist, one who deliberately and maliciously sets fire to property; bomb which ignites and burns; agitator, one who stirs up strife. pertaining to arson, of the deliberate burning of property; stirring up violence or strife, inflammatory. incendiaryin*cendi*a*ry, a. [l. incendiarius, fr. incendium a fire, conflagration: cf. f. incendiaire. see: incense to inflame.]