calm3 also calm down [intransitive and transitive]
to become quiet and relaxed after you have been angry, excited, nervous, or upset, or to make someone become quiet and relaxed:
He tried to calm the frightened children.
Calm down and tell me what happened.
We tried to calm people's fears.
calm yourself (down)
She lit a cigarette to calm herself down.
if a situation calms down, it becomes easier to deal with because there are fewer problems and it is not as busy as it was before:
It took months for things to calm down after we had the baby.