To become calm or quiet after being agitated or excited. After the excitement of the party, it took a while for the children to settle down.
To begin to live a quieter, more stable life, often by getting married or starting a family. After years of traveling, he decided it was time to settle down and start a family.
To establish a permanent residence or place of business. They decided to settle down in a small town after retiring.
To become familiar with and comfortable in a new environment or situation. It took her a few weeks to settle down in her new job.