talk down

Short definition from Wiktionary

Verb

1. 1
   To negotiate a lower price.
2. 2
   To verbally assist someone to land an aircraft.
3. 3
   To convince a person to cease a drastic action or response, such as a suicide attempt or act of rage.
4. 4
   To overcome by spoken argument.
5. 5
   To comfort someone experiencing a bad trip, to help them come down.