The Collaborative International Dictionary of English v.0.48:

Incendiary \In*cen"di*a*ry\, a. [L. incendiarius, fr. incendium
   a fire, conflagration: cf. F. incendiaire. See Incense to
   inflame.]
   [1913 Webster]
   1. Of or pertaining to incendiarism, or the malicious burning
      of valuable property; as, incendiary material; as
      incendiary crime.
      [1913 Webster]

   2. Tending to excite or inflame factions, sedition, or
      quarrel; inflammatory; seditious. --Paley.
      [1913 Webster]

   Incendiary device, a device designed to set a structure on
      fire; a firebomb.

   Incendiary shell, a bombshell. See Carcass, 4.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Incendiary \In*cen"di*a*ry\ (?; 277), n.; pl. Incendiaries.
   [L. incendiarius: cf. F. incendiaire. See Incense to
   inflame.]
   [1913 Webster]
   1. Any person who maliciously sets fire to a building or
      other valuable or other valuable property.
      [1913 Webster]

   2. A person who excites or inflames factions, and promotes
      quarrels or sedition; an agitator; an exciter.
      [1913 Webster]

            Several cities . . . drove them out as incendiaries.
                                                  --Bentley.
      [1913 Webster]

WordNet (r) 3.0 (2006):

incendiary
    adj 1: involving deliberate burning of property; "an incendiary
           fire"
    2: arousing to action or rebellion [syn: incendiary,
       incitive, inflammatory, instigative, rabble-rousing,
       seditious]
    3: capable of catching fire spontaneously or causing fires or
       burning readily; "an incendiary agent"; "incendiary bombs"
    n 1: a criminal who illegally sets fire to property [syn:
         arsonist, incendiary, firebug]
    2: a bomb that is designed to start fires; is most effective
       against flammable targets (such as fuel) [syn: incendiary
       bomb, incendiary, firebomb]

Moby Thesaurus II by Grady Ward, 1.0:

94 Moby Thesaurus words for "incendiary":
   Mafioso, Young Turk, agent provocateur, agitational, agitative,
   agitator, agitprop, arsonist, beast, beldam, berserk, berserker,
   bomber, brute, catalyst, demagogue, demon, devil, dragon,
   enkindling, exciter, fiend, fire worshiper, fire-eater, firebrand,
   firebug, fomenter, fomenting, fury, goon, gorilla, gunsel,
   hardnose, hell-raiser, hellcat, hellhound, hellion, holy terror,
   hood, hoodlum, hothead, hotspur, incentive, inciter, inciting,
   incitive, inflamer, inflaming, inflammative, inflammatory,
   instigating, instigative, instigator, killer, kindling, lighting,
   mad dog, madcap, mischief-maker, monster, mugger, provocateur,
   provoker, pyrolater, pyromaniac, pyrophile, rabble-rouser,
   rabble-rousing, rapist, revolutionary, ringleader, rouser, savage,
   seditionary, seditionist, she-wolf, spitfire, termagant, terror,
   terrorist, tiger, tigress, torch, tough, tough guy, troublemaker,
   ugly customer, urger, violent, virago, vixen, wild beast, witch,
   wolf



Bouvier's Law Dictionary, Revised 6th Ed (1856):

INCENDIARY, crim. law. One who maliciously and willfully sets another
person's house on fire; one guilty of the crime of arson.
     2. This offence is punished by the statute laws of the different states
according to their several provisions. The civil law punished it with death,
Dig. 47, 9, 12, 1, by the offender being cast into the fire. Id. 48, 19, 28,
12; Code, 9, 1, 11. Vide Dane's Ab. Index, h.t.