sich beruhigen
to calm down
To become calm and composed again after being excited, anxious, or angry.
Atme tief durch und versuche, dich zu beruhigen.
Take a deep breath and try to calm down.

to calm
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to calm down
To become calm and composed again after being excited, anxious, or angry.
Atme tief durch und versuche, dich zu beruhigen.
Take a deep breath and try to calm down.

The verb 'beruhigen' (to calm) is formed from the adjective 'ruhig' (calm/quiet) and the prefix 'be-'. It literally means 'to make calm'.
Die Musik hatte eine beruhigende Wirkung auf ihn.
The music had a calming effect on him.
This verb can be used reflexively or transitively. 'Sich beruhigen' (to calm down) means that you yourself become calm again. 'Jemanden/etwas beruhigen' (to calm someone/something) means that you calm another person or a situation.
Nach dem Streit musste ich mich erst einmal beruhigen.
After the argument, I first had to calm down.
'Beruhigen' can also refer to abstract things. It is often used for situations, markets, or the weather. Then it means 'to stabilize' or 'to normalize'.
Die Zentralbank versuchte, die Finanzmärkte zu beruhigen.
The central bank tried to calm the financial markets.
to upset / excite
'aufregen' and 'beruhigen' are clear opposites. 'aufregen' means that someone becomes emotionally agitated, angry, nervous, or worried, or that something triggers this reaction. 'beruhigen' means the opposite: someone becomes calm again, or another person helps them do so. Both words can be used reflexively, for example 'sich aufregen' and 'sich beruhigen'. Memory tip: First you might get upset, and afterward you calm down again.

Mila hat den kleinen Jungen beim Arzt beruhigt.
Mila calmed the little boy at the doctor's office.
Die Kundin regt sich am Telefon über die falsche Rechnung auf.
The customer gets upset on the phone about the incorrect bill.