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]