The Collaborative International Dictionary of English v.0.48:

Tumefaction \Tu`me*fac"tion\, n. [Cf. F. tum['e]faction.]
   The act or process of tumefying, swelling, or rising into a
   tumor; a tumor; a swelling. --Arbuthnot.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tumefaction
    n 1: the process of tumefying; the organic process whereby
         tissue becomes swollen by the accumulation of fluid within
         it