from The American Heritage® Dictionary of the English Language, 4th Edition
- intransitive v. To utter the murmuring sound of a dove or pigeon or a sound resembling it.
- intransitive v. To talk fondly or amorously in murmurs: The visitors cooed over the newborn baby.
- transitive v. To express or utter with soft murmuring sounds.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The murmuring sound made by a dove or pigeon.
- v. To make a soft murmuring sound, as a pigeon.
- v. To speak in an admiring fashion, to be enthusiastic about.
- adj. cool
- interj. Expression of fright, surprise, approval, etc.
from the GNU version of the Collaborative International Dictionary of English
- intransitive v. To make a low repeated cry or sound, like the characteristic note of pigeons or doves.
- intransitive v. To show affection; to act in a loving way. See under Bill, v. i.
from The Century Dictionary and Cyclopedia
- To utter a low, plaintive, murmuring sound (imitated by the sound of the word) characteristic of pigeons or doves.
- Hence To converse affectionately, like cooing doves; make love in murmuring endearments: commonly in the phrase to bill and coo. See bill, v. i.
- To utter by cooing.
- To call.
- n. The characteristic murmuring sound uttered by doves and pigeons.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. the sound made by a pigeon
- v. cry softly, as of pigeons
- v. speak softly or lovingly
Imitative.(American Heritage® Dictionary of the English Language, Fourth Edition)
Of onomatopoetic/imitative origin. (Wiktionary)
Shortening of cool. Compare foo. (Wiktionary)