retrogression vs regression

retrogression and regression both are nouns.

Word	Noun	Adjective	Verb	Adverb
retrogression	Yes	No	No	No
regression	Yes	No	No	No

As nouns, retrogression and regression are synonyms defined as:

Other synonyms of retrogression include regress, retroversion, reversion.

retrogression (noun)	regression (noun)
returning to a former state	returning to a former state
passing from a more complex to a simpler biological form	the relation between selected values of x and observed values of y (from which the most probable value of y can be predicted for any value of x)
	(psychiatry) a defense mechanism in which you flee from reality by assuming a more infantile state
	an abnormal state in which development has stopped prematurely