coo

Short definition from Wiktionary

Noun

1. 1
   The murmuring sound made by a dove or pigeon.
2. 2
   An expression of pleasure made by a person.
3. 3
   Initialism of chief operating officer.
4. 4
   Initialism of country of origin.

Verb

1. 1
   To make a soft murmuring sound, as a pigeon.
2. 2
   To speak in an admiring fashion, to be enthusiastic about.

Adjective

1. 1
   Cool.

Interjection

1. 1
   An expression of approval, fright, surprise, etc.