The Collaborative International Dictionary of English v.0.48:

Necrosis \Ne*cro"sis\ (n[-e]*kr[=o]"s[i^]s), n. [NL., fr. Gr.
   ne`krwsis, fr. nekruy^n to make dead, to mortify, nekro`s a
   dead body.]
   1. (Med.) The pathologic death of part of a tissue due to
      irreversible damage. Contrast to necrobiosis, which is a
      normal death of cells in a tissue. Formerly, applied
      primarily to death of bone tissue.
      [1913 Webster +PJC]

   2. (Bot.) A disease of trees, in which the branches gradually
      dry up from the bark to the center.
      [1913 Webster]

WordNet (r) 3.0 (2006):

necrosis
    n 1: the localized death of living cells (as from infection or
         the interruption of blood supply) [syn: necrosis,
         mortification, gangrene, sphacelus]