Source : Webster's Revised Unabridged Dictionary (1913)

Introversion \In`tro*ver"sion\, n. [See {Introvert}.]
   The act of introverting, or the state of being introverted;
   the act of turning the mind inward. --Berkeley.

Source : WordNet®

introversion
     n 1: the condition of being folded inward or sheathed [syn: {invagination}]
     2: the folding in of an outer layer so as to form a pocket in
        the surface; "the invagination of the blastula" [syn: {invagination},
         {intussusception}, {infolding}]
     3: (psychology) an introverted disposition; concern with one's
        own thoughts and feelings [ant: {ambiversion}, {extraversion}]