Synonyms for Digressive (same or very similar meaning)
WordNet sense 1 (of superficial relevance if any):
tangential
WordNet sense 2 (having no bearing on or connection with the subject at issue):
irrelevant
WordNet sense 3 ((of e.g. speech and writing) tending to depart from the main point or cover a wide range of subjects):
discursive, excursive, rambling
WordNet sense 4 (extended senses; not direct in manner or language or behavior or action):
indirect
From the ODE community, based on WordNet
add/edit