The Collaborative International Dictionary of English v.0.48:

Combustion \Com*bus"tion\ (?; 106), n. [L. combustio: cf. F.
   combustion.]
   1. The state of burning.
      [1913 Webster]

   2. (Chem.) The combination of a combustible with a supporter
      of combustion, producing heat, and sometimes both light
      and heat.
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            Combustion results in common cases from the mutual
            chemical action and reaction of the combustible and
            the oxygen of the atmosphere, whereby a new compound
            is formed.                            --Ure.
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   Supporter of combustion (Chem.), a gas, as oxygen, the
      combination of which with a combustible, as coal,
      constitutes combustion.
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   3. Violent agitation; confusion; tumult. [Obs.]
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            There [were] great combustions and divisions among
            the heads of the university.          --Mede.
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            But say from whence this new combustion springs.
                                                  --Dryden.
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WordNet (r) 3.0 (2006):

combustion
    n 1: a process in which a substance reacts with oxygen to give
         heat and light [syn: combustion, burning]
    2: a state of violent disturbance and excitement; "combustion
       grew until revolt was unavoidable"
    3: the act of burning something; "the burning of leaves was
       prohibited by a town ordinance" [syn: burning,
       combustion]

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "combustion":
   backfire, balefire, beacon, beacon fire, blaze, blazing,
   blistering, bonfire, branding, burning, burning ghat, calcination,
   campfire, carbonization, cauterization, cautery, cheerful fire,
   cineration, concremation, conflagration, corposant, cozy fire,
   cracking, crackling fire, cremation, crematory, cupellation,
   death fire, deflagration, destructive distillation, distillation,
   distilling, fen fire, fire, flame, flaming, flashing point,
   flicker, flickering flame, forest fire, fox fire, funeral pyre,
   ignis fatuus, ignition, incineration, ingle, lambent flame,
   marshfire, open fire, oxidation, oxidization, parching,
   prairie fire, pyre, pyrolysis, raging fire, refining, scorching,
   scorification, sea of flames, searing, self-immolation,
   sheet of fire, signal beacon, singeing, smelting, smudge fire,
   suttee, the stake, thermogenesis, three-alarm fire, two-alarm fire,
   vesication, watch fire, wildfire, witch fire