The Collaborative International Dictionary of English v.0.48:

Cuckoo \Cuck"oo\ (k[oo^]k"[=oo]), n. [OE. coccou, cukkow, F.
   coucou, prob. of imitative origin; cf. L. cuculus, Gr. ????,
   Skr. k?ki?a, G. kuckuk, D. koekoek.] (Zool.)
   A bird belonging to Cuculus, Coccyzus, and several allied
   genera, of many species.
   [1913 Webster]

   Note: The European cuckoo (Cuculus canorus) builds no nest
         of its own, but lays its eggs in the nests of other
         birds, to be hatched by them. The American
         yellow-billed cuckoo (Coccyzus Americanus) and the
         black-billed cuckoo (Coccyzus erythrophthalmus) build
         their own nests.
         [1913 Webster]

   Cuckoo clock, a clock so constructed that at the time for
      striking it gives forth sounds resembling the cry of the
      cuckoo.

   Cuckoo dove (Zool.), a long-tailed pigeon of the genus
      Macropygia. Many species inhabit the East Indies.

   Cuckoo fish (Zool.), the European red gurnard (Trigla
      cuculus). The name probably alludes to the sound that it
      utters.

   Cuckoo falcon (Zool.), any falcon of the genus Baza. The
      genus inhabits Africa and the East Indies.

   Cuckoo maid (Zool.), the wryneck; -- called also cuckoo
      mate.

   Cuckoo ray (Zool.), a British ray (Raia miraletus).

   Cuckoo spit, or Cuckoo spittle.
   (a) A frothy secretion found upon plants, exuded by the
       larvae of certain insects, for concealment; -- called
       also toad spittle and frog spit.
   (b) (Zool.) A small hemipterous insect, the larva of which,
       living on grass and the leaves of plants, exudes this
       secretion. The insects belong to Aphrophora,
       Helochara, and allied genera.

   Ground cuckoo, the chaparral cock.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cuckoo
    n 1: a man who is a stupid incompetent fool [syn: fathead,
         goof, goofball, bozo, jackass, goose, cuckoo,
         twat, zany]
    2: any of numerous European and North American birds having
       pointed wings and a long tail
    v 1: repeat monotonously, like a cuckoo repeats his call

Moby Thesaurus II by Grady Ward, 1.0:

140 Moby Thesaurus words for "cuckoo":
   Philomel, ape, balmy, bananas, barmy, bats, batty, beany, bonkers,
   buggy, bughouse, bugs, bulbul, cackle, call, canary, carol, caw,
   chatter, cheep, chirk, chirp, chirr, chirrup, chitter, chuck,
   clack, cluck, cock-a-doodle-doo, conformist, coo, copier, copycat,
   copyist, counterfeiter, crackbrain, crackbrained, cracked,
   crackers, crank, cranky, crazed, crazy, croak, cronk, crow, daffy,
   daft, ding-a-ling, dippy, dissembler, dissimulator, dotty, drum,
   echo, echoer, echoist, faker, feathered songster, flaky, flipped,
   forger, freaked-out, fruitcakey, fruity, gabble, gaga, gaggle,
   gobble, goofy, guggle, harebrain, haywire, honk, hoo, hoot,
   hypocrite, imitator, impersonator, impostor, just plain nuts, kook,
   kooky, lark, loony, loopy, lunatic, mavis, mime, mimer, mimic,
   mimicker, mocker, mockingbird, monkey, nightingale, nut, nuts,
   nutty, off the hinges, off the track, off the wall, oriole, parrot,
   peep, phony, pip, pipe, plagiarist, poll-parrot, polly,
   polly-parrot, poseur, potty, quack, ringdove, roll, round the bend,
   scold, screwball, screwballs, screwy, sheep, simulator, sing,
   singing bird, slaphappy, song sparrow, songbird, songster, squawk,
   thrush, trill, tweet, twit, twitter, wacky, warble, warbler,
   whistle



Easton's 1897 Bible Dictionary:

Cuckoo
   (Heb. shahaph), from a root meaning "to be lean; slender." This
   bird is mentioned only in Lev. 11:16 and Deut. 14:15 (R.V.,
   "seamew"). Some have interpreted the Hebrew word by "petrel" or
   "shearwater" (Puffinus cinereus), which is found on the coast of
   Syria; others think it denotes the "sea-gull" or "seamew." The
   common cuckoo (Cuculus canorus) feeds on reptiles and large
   insects. It is found in Asia and Africa as well as in Europe. It
   only passes the winter in Palestine. The Arabs suppose it to
   utter the cry _Yakub_, and hence they call it _tir el-Yakub_;
   i.e., "Jacob's bird."