Cuck from cuckold, referring to the cuckoo, which lays its eggs in other birds' nests. Used since medieval times to refer to the husband of an adulterous wife, especially if she gives birth to another man's child. There is also the modern-day cuckold fetish, where a man receives sexual satisfaction from his wife or girlfriend being plowed vigorously by another man. In TD.win context it applies to traitors and sellouts, especially cucked Republicans and conservatives.