Synonyms for Digression (same or very similar meaning)
WordNet sense 1 (a message that departs from the main subject):
aside, parenthesis, divagation, excursusWordNet sense 2 (a turning aside (of your course or attention or concern)):
deflection, deviation, diversion, deflexionWordNet sense 3 (wandering from the main path of a journey):
excursionFrom the ODE community, based on WordNetadd/edit