involution

Etymology

From Latin involūtiō, from involvō.

noun

1. 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. 1938, Xavier Herbert, chapter V, in Capricornia, page 74
   ‘Gomez,’ said the mortician, ‘is an expert only on the involutions of his own rectum.’ 1968, Anthony Burgess, “Enderby Outside”, in The Complete Enderby, published 2002, page 302
2. 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. (mathematics) 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. 1996, Alfred J. Menezesm, Paul C. van Oorschot, Scott A. Vanstone, Handbook of Applied Cryptography, CRC Press, page 10
4. (medicine) The shrinking of an organ (such as the uterus) to a former size.
5. (physiology) The regressive changes in the body occurring with old age.
6. (mathematics, obsolete) A power: the result of raising one number to the power of another.
7. (economics, social sciences, of a society or nation) A cessation of development or progress despite intense inner competition.
8. (neologism, slang) A state of increased competition for limited resources, requiring great effort to stay ahead.