involution

noun involutions

1. countable, uncountable Entanglement; a spiralling inwards; intricacy. […]usually his attention was diverted from her feet by her shrieks of laughter and the astounding involutions of her huge brown-yellow frame.
2. countable, uncountable A complicated grammatical construction. 1917, James Huneker, Unicorns, New York: Scribner, Chapter 11 “Style and Rhythm in English Prose,” p. 129, Walter Pater’s essay on Style is honeycombed with involutions and preciosity.
3. countable, uncountable An endofunction whose square is equal to the identity function; a function equal to its inverse. Involutions have the property that they are their own inverses.
4. countable, uncountable The shrinking of an organ (such as the uterus) to a former size.
5. countable, uncountable The regressive changes in the body occurring with old age.
6. countable, obsolete, uncountable A power: the result of raising one number to the power of another.
7. countable, uncountable, of a society or nation A cessation of development or progress involving intense inner competition.
8. countable, neologism, uncountable A state of increased competition for limited resources, requiring great effort to stay ahead.
9. countable, uncountable The migration of a cell layer inward, sliding over an outer layer of cells. It occurs at gastrulation during embryogenesis.