(noun) a message that departs from the main subject. Synonyms: digression, aside, excursus, parenthesis.
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Noun Definition 1
(noun) a turning aside (of your course or attention or concern). Synonyms: diversion, deviation, digression, deflection, deflexion. Examples: "A diversion from the main highway." "A digression into irrelevant details." "A deflection from his goal."