Real Dictionary

talk down
phrasal verb: If someone talks down a particular thing, they make it less interesting, valuable, or likely than it originally seemed.
phrasal verb: To talk down someone who is flying an aircraft in an emergency means to give them instructions so that they can land safely.
phrasal verb: To talk someone down in negotiations means to persuade them to accept less money than they originally asked for.

talk down in American English
to overwhelm by force of argument or by loud and persistent talking; subdue by talking
to silence by talking louder, longer, or more effectively than

talk down in British English
to behave (towards) in a superior or haughty manner