What Is The Origin Of The F-word?

It's hard to be sure, although there are plenty of candidates.  The word may have come from various different words being blended together.  The F-word appears to have spread from Scotland into England, which would suggest a Scandinavian origin.  Fokken in Swedish dialect has the same meaning as the F-word in English.  Fokken in old Dutch meant to strike or copulate, although the modern usage means 'to breed' with reference to animals.   It may come from ficken or fucken, old German words that meant to hit or strike, and is related to Latin words for puncture or prick.  There was also a Latin slang word  futuere which meant to copulate.

Most lexicographers put the F-word down as Anglo-Saxon, which supports a German origin.

It was in usage by the 1500s to mean sexual intercourse, as evinced by a contemporary dictionary entry.