Wiktionary
vb. 1 (context idiomatic English) To negotiate a lower price. 2 (context idiomatic English) To speak condescendingly or as though the listener is inferior. 3 (context flying English) To tell an airplane passenger (who has had no flight training) step by step by two-way radio how to land the plane, e.g. if its pilot has become incapacitated while flying.
WordNet
v. belittle through talk
speak in a condescending manner, as if to a child; "He talks down to her"
Usage examples of "talk down".
She was young and vulnerable, and she didn't talk down to them, and they were half in love with her.
If the prince wanted to talk down to Andy any farther, he would have to get up on a ladder.
She was intelligent and beautiful and older, but she did not talk down to him.
Charity immediately perceived that something bitter had happened to him, and that he was trying to talk down the recollection.