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.