The Collaborative International Dictionary of English v.0.48:

Intumescence \In`tu*mes"cence\, n. [Cf. F. intumescence.]
   [1913 Webster]
   1. The act or process of swelling or enlarging; also, the
      state of being swollen; expansion; tumidity; especially,
      the swelling up of bodies under the action of heat.
      [1913 Webster]

            The intumescence of nations.          --Johnson.
      [1913 Webster]

   2. Anything swollen or enlarged, as a tumor.
      [1913 Webster]

WordNet (r) 3.0 (2006):

intumescence
    n 1: swelling up with blood or other fluids (as with congestion)
         [syn: intumescence, intumescency]
    2: the increase in volume of certain substances when they are
       heated (often accompanied by release of water) [syn:
       intumescence, intumescency, swelling]