The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

            The stockdove only through the forest cooes,
            Mournfully hoarse.                    --Thomson.
      [1913 Webster]

   2. To show affection; to act in a loving way. See under
      Bill, v. i. "Billing or cooing." --Byron.
      [1913 Webster] Cooey