Source : Webster's Revised Unabridged Dictionary (1913)

Intussusception \In`tus*sus*cep"tion\, n. [L. intus within +
   susception. Cf. {Introsusception}.]
   1. The reception of one part within another.

   2. (Med.) The abnormal reception or slipping of a part of a
      tube, by inversion and descent, within a contiguous part
      of it; specifically, the reception or slipping of the
      upper part of the small intestine into the lower;
      introsusception; invagination. --Dunglison.

   3. (Bot.) The interposition of new particles of formative
      material among those already existing, as in a cell wall,
      or in a starch grain.

   4. (Physiol.) The act of taking foreign matter, as food, into
      a living body; the process of nutrition, by which dead
      matter is absorbed by the living organism, and ultimately
      converted into the organized substance of its various
      tissues and organs.

            Dead bodies increase by apposition; living bodies by
            intrussusception.                     --McKendrick.

Source : WordNet®

intussusception
     n 1: the folding in of an outer layer so as to form a pocket in
          the surface; "the invagination of the blastula" [syn: {invagination},
           {introversion}, {infolding}]
     2: (biology) growth in the surface area of a cell by the
        deposit of new particles between existing particles in the
        cell wall