The Collaborative International Dictionary of English v.0.48:

Amitosis \Am`i*to"sis\, n. [NL. See A- not, and Mitosis.]
   (Biol.)
   Cell division in which there is first a simple cleavage of
   the nucleus without change in its structure (such as the
   formation of chromosomes), followed by the division of the
   cytoplasm; direct cell division; -- opposed to mitosis. It
   is not the usual mode of division, and is believed by many to
   occur chiefly in highly specialized cells which are incapable
   of long-continued multiplication, in transitory structures,
   and in those in early stages of degeneration.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

amitosis
    n 1: the direct method of cell division characterized by simple
         division of the nucleus without formation of chromosomes