involution

in·vo·lu·tion

noun \ˌin-və-ˈlü-shən\

Definition of INVOLUTION

1

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

2

: a shrinking or return to a former size <involution of the uterus after pregnancy>

3

: the regressive alterations of a body or its parts characteristic of the aging process; specifically : decline marked by a decrease of bodily vigor and in women by menopause