Croon

Part of speech: noun (n.)

1. A low, continued moan; a murmur.

2. A low singing; a plain, artless melody.

Part of speech: verb (v.)

1. To make a continuous hollow moan, as cattle do when in pain. [Scot.] Jamieson.

2. To hum or sing in a low tone; to murmur softly. Here an old grandmother was crooning over a sick child, and rocking it to and fro. Dickens.

Part of speech: verb (v.)

1. To sing in a low tone, as if to one's self; to hum. Hearing such stanzas crooned in her praise. C. Bront

2. To soothe by singing softly. The fragment of the childish hymn with which he sung and crooned himself asleep. Dickens.