digression vs excursus

digression and excursus both are nouns.

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

As nouns, digression and excursus are synonyms defined as:

Other synonyms of digression include aside, divagation, parenthesis.

digression (noun)	excursus (noun)
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