“Natiform” listed on page 30 of volume VI, part II (M–N), § ii (N) of A New English Dictionary on Historical Principles [1st ed., 1908] Natiform (nēⁱ·tifǭɹm), a. [f. L. nat-is (see Nates) + -(i)form.] Resembling or having the form of buttocks. [¶] 1681 tr. Willis’ Rem. Med. Wks. Vocab., Natiform, in the form of a buttock. 1839–47Todd’s Cycl. Anat. III. 384/1 The natiform protuberances are unusually large. 1898Dawson WilliamsMed. Dis. Inf. 262 The skull assumes a peculiar and characteristic shape, to which the term natiform has been applied.
“natiform, a.” listed in the Oxford English Dictionary [2nd ed., 1989]
“† natiform, adj.” listed in the Oxford English Dictionary [3rd ed., December 2003]