digress

Verb

• wander from a direct or straight course

• lose clarity or turn aside especially from the main subject of attention or course of argument in writing, thinking, or speaking
  • She always digresses when telling a story
    
  • her mind wanders
    
  • Don't digress when you give a lecture
    

Related words

• Synonyms: 
  sidetrack , depart , straggle , stray , divagate , wander