Origin: 1480–90; earlier hach-boon (with spurious h-); (h)ach variant by misdivision as an (h)ach(e) of a nache rump < Middle French < Vulgar Latin *natica, feminine of *naticus of the rump, equivalent to Latin nati(s) rump, nates + -cus adj. suffix
[C15 hach-boon, altered from earlier nache-bone, nage-bone (a nache mistaken for an ache, an aitch; compare adder1); nache buttock, via Old French from Late Latin natica, from Latin natis buttock]