Source : Webster's Revised Unabridged Dictionary (1913)

Natch \Natch\, n. [OF. nache fesse, LL. natica, from L. natis
   the rump, buttocks. Cf. {Aitchbone}.]
   The rump of beef; esp., the lower and back part of the rump.

   {Natch bone}, the edgebone, or aitchbone, in beef.