Coo (verb)

1. Make a soft, murmuring sound expressing affection or contentment.
2. Speak softly and tenderly.

Origin:

Early 16th century: imitative.

Examples:

1. The doves cooed in the background.
2. She cooed to the baby to calm him down.
3. The pigeon cooed softly on the windowsill.
4. He cooed sweet nothings in her ear.
5. The baby cooed happily in his mother's arms.