(1):
(n.) The reception of one part within another.
(2):
(n.) 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.
(3):
(n.) The interposition of new particles of formative material among those already existing, as in a cell wall, or in a starch grain.
(4):
(n.) 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.