noun

1. a regressing, or going back; return; movement backward
2. retrogression
3. Astron. the slow westward shifting of the nodes of an orbit, caused by a perturbation: the complete cycle of the regression of the nodes of the moon's orbit around the earth takes about 18.6 years
4. Biol. reversion to an earlier or simpler form, or to a general or common type
5. Med. a gradual subsiding of a disease or its symptoms
6. Psychoanalysis reversion to earlier or more infantile behavior patterns
7. Statistics an estimation technique in which functions or coefficients within functions are designed to estimate values of a dependent variable

Etymology: L regressio