Coo \Coo\, v. i. [imp. & p. p. Cooed; p. pr. & vb. n. Cooing.]

1. To make a low repeated cry or sound, like the characteristic note of pigeons or doves.

The stockdove only through the forest cooes, Mournfully hoarse. --Thomson.

2. To show affection; to act in a loving way. See under Bill, v. i. ``Billing or cooing.'' --Byron.

Source: Webster's Revised Unabridged Dictionary (1913)