fuck a difficult word to trace, in part because it was taboo to the editors of the original OED when the "F" volume was compiled, 1893-97. Written form only attested from early 16c. OED 2nd edition cites 1503, in the form fukkit; earliest appearance of current spelling is 1535 -- "Bischops ... may fuck thair fill and be vnmaryit"
, but presumably it is a much more ancient word than that, simply one that wasn't likely to be written in the kind of texts that have survived from O.E. and M.E. Buck cites proper name John le Fucker from 1278. The word apparently is hinted at in a scurrilous 15c. poem, titled "Flen flyys," written in bastard L. and M.E. The relevant line reads:
Non sunt in celi
quia fuccant uuiuys of heli
"They are not in heaven because they fuck the wives of Ely." Fuccant is pseudo-L., and in the original it is written in cipher.
http://www.etymonline.com/index.php?search=fuck&searchmode=none
Etymologies can be pretty interesting. I wonder what happended to those other texts.