kuckold

Cuckold is a historic derogatory term for a man who has an unfaithful wife. The word, which has been in recorded use since the 13th century, derives from the cuckoo which gives up nurturing its own by laying eggs in other birds' nests.[citation needed]

In modern terms, a cuckold can also mean a male fetishist who gains sexual gratification from watching his wife, partner or significant other have intercourse with other people