coo

To kiss, nuzzle, and talk sweetly with another person, typically a romantic partner. All my sister and her boyfriend do is bill and coo—it's so nauseating. Hi, the rest of us who are single don't appreciate all your billing and cooing, thanks. A: "Ugh, why do they have to bill and coo so much?" B: "They're teenagers in love. They're not capable of much else right now."

slang Crazy. There's a guy on our corner who shouts about the end of the world; I think he's a little cuckoo. You can't tell people you want to start a business selling bees as pets—they'll think you're cuckoo! I don't know why she yelled at me like that—she just went cuckoo all of a sudden.

If two lovers bill and coo, they kiss and talk together in a loving way. I just have to stand there grinding my teeth while they bill and coo. Note: In this expression, lovers are being compared to a pair of doves touching their beaks or bills together and cooing.

To kiss or caress and murmur endearments.

To hug and kiss. A sweet old-fashioned phrase for necking, making out, smooching, or playing kissy-face—the way that courting birds touch bills and emit soft cooing noises before they get down to the real mating game.