regress vs retrogress

regress is a noun but retrogress is not a noun.

Word	Noun	Adjective	Verb	Adverb
regress	Yes	No	Yes	No
retrogress	No	No	Yes	No

As verbs, regress and retrogress are synonyms defined as:

Other synonyms of regress include fall back, lapse, recidivate, relapse.

As verbs, regress and retrogress are synonyms defined as:

Other synonyms of regress include retrograde.

As verbs, retrogress is a hyponym of regress; that is, retrogress is a word with a more specific, narrower meaning than regress:

Other hyponyms of regress include fall back, lapse, recidivate, regress, relapse, resile, go back, recover, recuperate.

regress (noun)	retrogress (noun)
returning to a former state
the reasoning involved when you assume the conclusion is true and reason backward to the evidence

regress (verb)	retrogress (verb)
go back to bad behavior	go back to bad behavior
get worse or fall back to a previous condition	get worse or fall back to a previous condition
go back to a previous state
go back to a statistical means