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.
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   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]