The Collaborative International Dictionary of English v.0.48:

Apostemation \A*pos`te*ma"tion\, n. [LL. apostematio: cf. F.
   apost['e]mation.] (Med.)
   The formation of an aposteme; the process of suppuration.
   [Written corruptly imposthumation.] --Wiseman.
   [1913 Webster]