"Billed coo" is a phrase that refers to the distinctive sound that a pigeon or dove makes. There are many synonyms that can be used to describe this sound. Some of the most common synonyms include cooing, murmuring, coochie-cooing, and trilling. Other synonyms include warbling, chirping, babbling, and singing. Each of these words describes a particular type of vocalization that pigeons and doves make, and they can be used interchangeably depending on the context. Whether you are describing the sound of a bird in the wild or using the phrase to convey a feeling of calm or comfort, there is a synonym available for every occasion.