to be quiet and undisturbed: to settle into calm and stay free of turmoil
This verb describes the calm that comes when trouble stops. It is not the quiet of silence so much as the quiet of a storm passing, of fighting ending, of a restless person finally settling down. Whatever was stirred up has gone still.
Its most famous use is a refrain in the history books: after a deliverer wins a battle, "the land had rest." The country is no longer overrun by enemies, so life can resume in peace. The same calm can settle on a single person who stops worrying, on a people living securely in their own place, or even on something physical like wine left to settle or a stilled sea.
In its causative forms the word turns outward: God or a person gives this calm to someone else, or holds steady and keeps calm rather than reacting in panic or rage. The book of Isaiah turns it into a quiet trust in God: strength is found not in frantic action but in staying still and confident.
The senses below are all the same calm seen from different angles, depending on who or what is being quieted.