Real Dictionary

coo
verb: When a dove or pigeon coos, it makes the soft sounds that doves and pigeons typically make.

COO in American English
abbreviation: chief operating officer

coo in American English 1
to make the soft, murmuring sound of pigeons or doves, or a sound like this
intransitive verb: to utter or imitate the soft, murmuring sound characteristic of doves
noun: a cooing sound
transitive verb: to utter by cooing

coo in American English 2
used variously to express surprise, doubt, delight, etc.
interjection: (used to express surprise or amazement)

coo in British English
abbreviation for: chief operating officer
abbreviation for: cost of ownership
exclamation: an exclamation of surprise, awe, etc
noun: the executive in charge of day-to-day operations in an organization
noun: the sound of cooing
verb: (of doves, pigeons, etc) to make a characteristic soft throaty call