"Talk down" has 8 definitions. The phrasal verb can be separated for most of them.
I also explain any subtle differences to other similar phrases.
1. To talk about something in a way that that makes it seem less important or less serious than it really is.
However, I think that other vocabulary, like "downplay" or "minimise," that have the same meaning are more common.
"Climate change is often talked down, even at environmental conferences."
"You can't afford to talk your achievements down when you're in a job interview."
"Brush aside" or "Talk down"
A similar phrasal verb is "brush aside something," which means to refuse to consider something seriously because it's considered unimportant.
For "talk down," an issue might be talked about but it is either made to look less serious or less important, or its seriousness or importance is not made clear.
With "brush aside," usually this means that something is ignored.
"He talked down his father's criminal history."
This means he made the issue less serious than it actually is.
"He brushed aside his father's criminal history."
This means he ignored the issue and did not address it.
2. To persuade someone that they are wrong or not to act.
This is considered American English.
"His lawyers talked down the CEO's intention to sell the company."
"I spent the whole day talking him down from going back to his ex."
3. To talk loudly to prevent someone else from speaking.
This is usually considered disapproving, but can sometimes be used as a kind of retaliation if the person they are talking down to was rude.
"My coworker tried to explain what actually happened but our boss talked her down."
"Eve started talking him down after she had enough of his offhand remarks about her looks."
"Talk at" or "Talk down"
A similar phrasal verb is "talk at," which means to speak to someone without listening to that person, or to speak to someone in a way that indicates a response is unwanted or not desired.
To me, "talk down" is more obvious and the intention to shut someone up is quite clear - sometimes by interrupting or talking loudly.
"Talk at" can be more subtle. Rather than shutting someone up, there is no invitation for the other person to respond. When there are responses, they are not really acknowledged.
"My boss kept talking us down every time we tried to say something."
This means the boss is preventing others from speaking by interrupting and speaking over others without letting them finish.
"My boss kept talking at us about the new project."
This means the boss kept on talking about the new project without asking for or acknowledging the contributions of others.
4. To persuade someone not to jump down from a high place.
"One of the residents spent two hours talking a guy down from the top of the building."
5. (informal) To calm someone not to do something extreme or harmful.
Maybe they have taken an illicit drug or they are having an episode due to a mental health disorder.
"The paramedic tried to talk him down by talking about his family."
"Triple zero call-takers are trained to talk down people who are considering harming themselves."
6. To explain to someone flying a plane how to land it through the radio, when the pilot has died or is incapacitated.
"People on the ground talked the pilot down when his navigation equipment stopped working."
"One of the passengers had to be talked down by air traffic controllers when the pilot passed out."
7. To persuade someone to lower the price of something.
"I managed to talk down the salesman to give me a discount."
"The client tried to talk me down but I said it was my final offer."
8. "Talk down to (someone)" - to talk to someone as if they are less intelligent or less important than you.
This one is inseparable with the preposition "to."
"It's sad that essential workers are often talked down to."
"There's no need to talk down to her - she knows what she's doing."