The Collaborative International Dictionary of English v.0.48:

Necrobiosis \Nec`ro*bi*o"sis\, n. [NL., fr. Gr. nekro`s dead + ?
   way of life, fr. ? life.] (Biol. & Med.)
   The death of a part of an organism by molecular
   disintegration and without loss of continuity, as in the
   processes of degeneration and atrophy; a normal dying out of
   cells in a tissue, in contrast to necrosis. --Virchow.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

necrobiosis
    n 1: (physiology) the normal degeneration and death of living
         cells (as in various epithelial cells) [syn: necrobiosis,
         cell death]