A bird belonging to Cuculus, Coccyzus, and several allied genera, of many species.
- A grayish European bird (Cuculus canorus) that has a characteristic two-note call and lays its eggs in the nests of birds of other species.
- Any of various related birds of the family Cuculidae, having grayish-brown plumage and a slender body.
- The call or cry of one of these birds.
- Slang A foolish or crazy person.
- To repeat incessantly, as a cuckoo does its call.
- Slang Lacking in sense; foolish or crazy.