cuckoo:  So distinctive is the cuckoo’s call that it is not always clear whether the names for the bird in various languages, based on the call, owe their similarity to borrowing or coincidence – Dutch, for instance, has koekoek, Russian kukúshka, Latin cuculus, and Greek kókkūx. In the case of English cuckoo, it seems to have been borrowed from Old French cucu, which was of imitative origin. Its first appearance is in the famous Cuckoo song of the late 13th century (‘Sumer is icumen in, lhude sing, cuccu!’), where it replaced the native Middle English word yeke (from Old English gēac, also of imitative origin).
mid-13c., from Old French cocu "cuckoo," also "cuckold," echoic of the male bird's mating cry (compare Greek kokkyx, Latin cuculus, Middle Irish cuach, Sanskrit kokilas). Slang adjectival sense of "crazy" is American English, 1918, but noun meaning "stupid person" is recorded by 1580s, perhaps from the bird's unvarying, oft-repeated call. The Old English name was geac, cognate with Old Norse gaukr, source of Scottish and northern English gowk. The Germanic words presumably originally were echoic, too, but had drifted in form. Cuckoo clock is from 1789.