The Collaborative International Dictionary of English v.0.48:

Manna croup \Man"na croup`\ (m[a^]n"n[.a] kr[=oo]p`). [Manna +
   Russ. & Pol. krupa groats, grits.]
   1. The portions of hard wheat kernels not ground into flour
      by the millstones: a kind of semolina prepared in Russia
      and used for puddings, soups, etc. -- called also manna
      groats.
      [1913 Webster]

   2. The husked grains of manna grass.
      [1913 Webster]