noun (n)

• a message that departs from the main subject(noun.communication)

  Synonym:
  aside, digression, excursus, parenthesis
  

  source: wordnet30
• a turning aside (of your course or attention or concern)(noun.act)

  Synonym:
  deflection, deflexion, deviation, digression, diversion
  

  source: wordnet30
• A wandering about or going astray; digression.(noun)

  source: webster1913