digressive, tangential -- (of superficial relevance if any; "a digressive allusion to the day of the week"; "a tangential remark")
digressive, discursive, excursive, rambling -- ((of e.g. speech and writing) tending to depart from the main point or cover a wide range of subjects; "amusingly digressive with satirical thrusts at women's fashions among other things"; "a rambling discursive book"; "his excursive remarks"; "a rambling speech about this and that")
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