parenthesis vs digression

parenthesis and digression both are nouns.

Word	Noun	Adjective	Verb	Adverb
parenthesis	Yes	No	No	No
digression	Yes	No	No	No

As nouns, parenthesis and digression are synonyms defined as:

parenthesis and digression: a message that departs from the main subject

Other synonyms of parenthesis include aside, divagation, excursus.

parenthesis (noun)	digression (noun)
either of two punctuation marks (or) used to enclose textual material	a turning aside (of your course or attention or concern)
a message that departs from the main subject	wandering from the main path of a journey
	a message that departs from the main subject