Cuckoo and cuckold are related words. Cuckold derives from the cuckoo's practice of laying an egg in another bird's nest. Usage found in the 13th century.

Cuckoo, applied to an insane person, originally was U. S. slang and is first found in print in 1918. Not admitted to the Oxford English Dictionary until the 1987 edition. Even as late as Gomme's time, an Englishman would relate the word in the rhyme to a cuckolding.