involution

noun

1. 1

   Entanglement; a spiralling inwards; intricacy.

2. 2

   A complicated grammatical construction.

3. 3

   An endofunction whose square is equal to the identity function; a function equal to its inverse.

4. 4

   The shrinking of an organ (such as the uterus) to a former size.

5. 5

   The regressive changes in the body occurring with old age.

6. 6

   A power: the result of raising one number to the power of another.