cuckoo many cuckoos lay their eggs in the nests of small songbirds; the cuckoo fledgling, once hatched, pushes the songbird fledglings out of the nest, giving rise to the phrase cuckoo in the nest (see below).

In Britain the first call of the cuckoo (a migratory bird) is traditionally a sign of spring.
cuckoo clock a clock that strikes the hour with a sound like a cuckoo's call and typically has a mechanical cuckoo that emerges with each note. It is often popularly associated with Switzerland, as in the lines added by Orson Welles to Grahame Greene's screenplay for The Third Man (1949 film), ‘In Switzerland they had brotherly love, five hundred years of democracy and peace and what did that produce…? The cuckoo clock.’
cuckoo in the nest an unwelcome intruder in a place or situation.

See also cuckold.

cuck·oo / ˈkoōkoō; ˈkoŏkoō/ • n. 1. a medium-sized long-tailed bird, typically with a gray or brown back and barred or pale underparts. The cuckoo family (Cuculidae) also includes roadrunners and anis. 2. inf. a crazy person.• adj. inf. crazy.

cuckoo Widely distributed forest bird. Related species are the ani, road runner and coucal. Noted for parasitic behaviour. Their chief food is insects. True Old World cuckoos are generally brownish, although a few species are brightly coloured. Length: 15–75cm (6–30in). Family Cuculidae; genus Cuculus.

cuckoo. Simple 2-note wind instr., imitating call of the bird, used in Toy Syms.

cuckoo XIII. — OF. cucu (mod. coucou); of imit. orig.