Bill and coo is a phrase that refers to a synonym for romantic or affectionate behavior usually demonstrated by birds. The phrase can also be used metaphorically to describe a couple's behavior. If you're searching for synonyms for bill and coo, consider phrases like "whisper sweet nothings," "display amorously," or "show affectionate gestures." Examples of synonyms to describe this lovey-dovey behavior are also "cooing and wooing," "making googly eyes," or "acting lovey-dovey." Bill and coo also reminds one of pigeons, which tend to exchange quiet, low-pitched sounds as a sign of affection, so appropriate synonyms for displaying affection include expressions like "purring, trilling, or cooing".