The Collaborative International Dictionary of English v.0.48:

Combust \Com*bust"\, a. [L. combustus, p. p. of comburere to
   burn up; com- + burere (only in comp.), of uncertain origin;
   cf. bustum funeral pyre, prurire to itch, pruna a live coal,
   Gr. pyrso`s firebrand, Skr. plush to burn.]
   1. Burnt; consumed. [Obs.] --Chaucer.
      [1913 Webster]

   2. (Astron.) So near the sun as to be obscured or eclipsed by
      his light, as the moon or planets when not more than eight
      degrees and a half from the sun. [Obs.]
      [1913 Webster]

            Planets that are oft combust.         --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

combust
    v 1: cause to burn or combust; "The sun burned off the fog"; "We
         combust coal and other fossil fuels" [syn: burn,
         combust]
    2: start to burn or burst into flames; "Marsh gases ignited
       suddenly"; "The oily rags combusted spontaneously" [syn:
       erupt, ignite, catch fire, take fire, combust,
       conflagrate]
    3: get very angry and fly into a rage; "The professor combusted
       when the student didn't know the answer to a very elementary
       question"; "Spam makes me go ballistic" [syn: flip one's
       lid, blow up, throw a fit, hit the roof, hit the
       ceiling, have kittens, have a fit, combust, blow
       one's stack, fly off the handle, flip one's wig, lose
       one's temper, blow a fuse, go ballistic]
    4: cause to become violent or angry; "Riots combusted Pakistan
       after the U.S. air attacks on Afghanistan"
    5: undergo combustion; "Maple wood burns well" [syn: burn,
       combust]