word has probable cognates in other Germanic languages, such as German ficken (to fuck); Dutch fokken (to breed, to strike, to beget); dialectal Norwegian fukka (to copulate), and dialectal Swedish fokka (to strike, to copulate) and fock (penis). This points to a possible etymology where Common Germanic fuk– comes from an Indo-European root meaning "to strike", cognate with non-Germanic words such as Latin pugnus "fist". By reverse application of Grimm's law, this hypothetical root has the form *pug–. In early Proto-Germanic the word was likely used at first as a slang or euphemistic replacement for an older word for intercourse, and then became the usual word for intercourse.
Yet another possible etymology is from the Old High German word pfluog, meaning "to plow, as in a field".