excursus vs parenthesis

excursus and parenthesis both are nouns.

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

As nouns, excursus and parenthesis are synonyms defined as:

Other synonyms of excursus include aside, digression, divagation.

excursus (noun)	parenthesis (noun)
a message that departs from the main subject	either of two punctuation marks (or) used to enclose textual material
	a message that departs from the main subject