An Etymological Dictionary of the German Language/Annotated/Kuckuck
Kuckuck, masculine, ‘cuckoo,’ from the equivalent late Middle High German kuckuk (rare), masculine; the usual term in Middle High German is gouch, which was introduced in the 15th century from Dutch (koekoek, early Middle Dutch cuccûc). An onomatopoetic term widely diffused, but it is not necessary to assume that it was borrowed in most of the languages, English cuckoo, French coucou, Latin cuculus, Welsh and Cornish cog, Or. cúach. See also Küchlein.