"digress" in the verb sense
1. digress, stray, divagate, wander
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"
2. sidetrack, depart, digress, straggle
wander from a direct or straight course
Source: WordNet® (An amazing lexical database of English)
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