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

Source: The Collaborative International Dictionary of English v.0.48
 

92 Moby Thesaurus words for "coo": aspirate, bark, bawl, bellow, blare, blat, blubber, boom, bray, breathe, buzz, cackle, call, carol, caw, chant, chatter, cheep, chirk, chirp, chirr, chirrup, chitter, chuck, clack, cluck, cock-a-doodle-doo, croak, cronk, crow, cuckoo, drawl, drum, exclaim, flute, gabble, gaggle, gasp, gobble, growl, grunt, guggle, hiss, honk, hoo, hoot, keen, lilt, maffle, mumble, murmur, mussitate, mutter, pant, peep, pip, pipe, quack, roar, roll, rumble, scold, scream, screech, shriek, sibilate, sigh, sing, snap, snarl, snort, sob, squall, squawk, squeal, susurrate, thunder, trill, trumpet, twang, tweet, twit, twitter, wail, warble, whine, whisper, whistle, yap, yawp, yell, yelp

Source: Moby Thesaurus II by Grady Ward, 1.0
 

coo

Source: WordNet (r) 2.0
 

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)