An excursus (from Latin excurrere, "to run out of") is a short episode or anecdote in a work of literature. Often excursuses have nothing to do with the matter being discussed by the work, and are used to lighten the atmosphere in a tragic story, similar to the role of satyr plays in Greek theatre. Sometimes they're used to provide backstory to the matter being discussed at hand, as in Pseudo-Apollodorus' Bibliotheke. Etymologies as excursuses Sometimes detailed or fanciful etymologies are use… (More on Excursus)