“Cuckold: The husband of an adulterous wife. The name derives from cuckoo, the chief characteristic of this bird being to deposit its eggs in other birds’ nests. Dr. Johnson explained that ‘it was usual to alarm a husband at the approach of an adulterer by calling Cuckoo, which by mistake was applied in time to the person warned.’ The cuckold was traditionally supposed to wear horns as the attribute of his condition. The usage is ancient; the Romans used to call an adulterer a cuckoo.”
Excerpted from: Murphy, Bruce, ed. Benet’s Reader’s Encyclopedia, Fourth Edition. New York: Harper Collins, 1996.