Source : Webster's Revised Unabridged Dictionary (1913)

Involution \In`vo*lu"tion\, n. [L. involutio: cf. F. involution.
   See {Involve}.]
   1. The act of involving or infolding.

   2. The state of being entangled or involved; complication;
      entanglement.

            All things are mixed, and causes blended, by mutual
            involutions.                          --Glanvill.

   3. That in which anything is involved, folded, or wrapped;
      envelope. --Sir T. Browne.

   4. (Gram.) The insertion of one or more clauses between the
      subject and the verb, in a way that involves or
      complicates the construction.

   5. (Math.) The act or process of raising a quantity to any
      power assigned; the multiplication of a quantity into
      itself a given number of times; -- the reverse of
      evolution.

   6. (Geom.) The relation which exists between three or more
      sets of points, a.a', b.b', c.c', so related to a point O
      on the line, that the product Oa.Oa' = Ob.Ob' = Oc.Oc' is
      constant. Sets of lines or surfaces possessing
      corresponding properties may be in involution.

   7. (Med.) The return of an enlarged part or organ to its
      normal size, as of the uterus after pregnancy.

Source : WordNet®

involution
     n 1: reduction in size of an organ or part (as in the return of
          the uterus to normal size after childbirth)
     2: a long and intricate and complicated grammatical
        construction
     3: marked by elaborately complex detail [syn: {elaborateness},
        {elaboration}, {intricacy}]
     4: the act of sharing in the activities of a group; "the
        teacher tried to increase his students' engagement in
        class activities" [syn: {engagement}, {participation}, {involvement}]
        [ant: {non-engagement}, {non-engagement}, {non-engagement}]
     5: the process of raising a quantity to some assigned power
        [syn: {exponentiation}]
     6: the action of enfolding something [syn: {enfolding}]