cuckold /KUK-əld/. noun or verb. A man whose spouse has been unfaithful or the act making a cuckold of someone. Of late, a scornful political term embraced most strongly by white nationalists to describe their opponents, often abbreviated as cuck. From Middle English cukeweld (same meaning), from Old French cucuault: cocu (cuckoo) + pejorative suffix -ault.
The interesting aspect of the etymology is its roots in the behavior of the female cuckoo bird, some of which lay their eggs in the nests of—and leave them to be cared for by—other birds, leading to the figurative word we are becoming all too familiar with today.