involution

1a (1) :  the act or an instance of enfolding or entangling :  involvement (2) :  an involved grammatical construction usually characterized by the insertion of clauses between the subject and predicateb :  complexity, intricacy

2 :  exponentiation

3a :  an inward curvature or penetrationb :  the formation of a gastrula by ingrowth of cells formed at the dorsal lip

4 :  a shrinking or return to a former size

5 :  the regressive alterations of a body or its parts characteristic of the aging process skeletal involution due to loss of estrogens at menopause