Croon (verb)

1. Sing in a soft, soothing voice, especially to a baby or a slow melody.
2. Sing popular songs in a soft, sentimental manner.

Origin:

Early 20th century: imitative.

Examples:

1. She crooned a lullaby to the baby.
2. He crooned a love song to his girlfriend.
3. The singer crooned the ballad with great emotion.
4. The band leader crooned a swing tune.
5. She crooned the melody with a gentle voice.