Lullaby (noun)

1. A soothing song or piece of music, typically one sung to children before they go to sleep.
2. A soothing sound or action that helps someone to sleep.

Origin:

Mid 16th century: from lull + bye.

Examples:

1. She sang a lullaby to her baby as she rocked him to sleep.
2. The lullaby was a traditional nursery rhyme passed down through the family.
3. The sound of the ocean was a natural lullaby for the baby.
4. The lullaby was a soothing melody that helped the baby to sleep.
5. The lullaby was a gentle song that was passed down from generation to generation.