Other forms: de-escalating; de-escalated
When something de-escalates, it's turned down a notch, becoming quieter or calmer. If you want to de-escalate an argument between siblings you're babysitting, you might try giving them both a popsicle.
In politics, de-escalating a situation can be a matter of life and death, as when mediators help de-escalate a conflict in order to avoid a war between two countries or groups. Whenever someone de-escalates an argument, they take something with potential to turn ugly or even violent and tone things down so that the issues can be calmly discussed. Police officers, diplomats, and elementary school teachers all need to learn to de-escalate intense situations.