Meaning 1 · most common
become calm
To become quiet, relaxed, or less active, especially after being excited or upset.
Examples
After the teacher entered the room, the students quickly settled down.
A: The kids are running everywhere!
B: Don’t worry, they’ll settle down once the movie starts.
Common mistake
Not: The kids couldn't settle down themselves.
Say: The kids couldn't settle down.
Intransitive here — no reflexive object; you don't 'settle down yourself'.
More on “become calm”Another example · Tell it apart · Goes with · Tip
Another example
When I feel stressed before an exam, I try to take deep breaths to help myself settle down.
Tell it apart
The class settled down after the bell.
They settled down in a small town.
Goes with
- settle down