The Collaborative International Dictionary of English v.0.48:

Intumesce \In`tu*mesce"\, v. i. [imp. & p. p. Intumesced; p.
   pr. & vb. n. Intumescing.] [L. intumescere; pref. in- in +
   tumescere to swell up, incho. fr. tumere to swell. See
   Tumid.]
   To enlarge or expand with heat; to swell; specifically, to
   swell up or bubble up under the action of heat, as before the
   blowpipe.
   [1913 Webster]

         In a higher heat, it intumesces, and melts into a
         yellowish black mass.                    --Kirwan.
   [1913 Webster]

WordNet (r) 3.0 (2006):

intumesce
    v 1: move upwards in bubbles, as from the effect of heating;
         also used metaphorically; "Gases bubbled up from the
         earth"; "Marx's ideas have bubbled up in many places in
         Latin America" [syn: bubble up, intumesce]
    2: expand abnormally; "The bellies of the starving children are
       swelling" [syn: swell, swell up, intumesce, tumefy,
       tumesce]