Bill and coo

To nuzzle affectionately and whisper endearments dates from 1816 according to the OED but that would be its first appearance in print. Billing and cooing mirrors the behaviour of doves, one of the species of birds that mates for life with the one partner. The verb to bill applies to birds and means to stroke with the bill and by Shakespeare’s time, it was being used figuratively to caress, as in his poem Venus and Adonis, line 381, “like two silver doves that sit a-billing” and again in Troilus and Cressida, Act III, Scene II, “What, billing again?” The verb to coo dates from 1670 the OED tells us, imitative of the soft murmuring sounds characteristic of doves. Therefore, both bill and coo have been around for such a long time that their coupling as late as 1816 seems hard to believe.