The Collaborative International Dictionary of English v.0.48:

Johnson grass \John"son grass`\ [Named after W. Johnson of
   Alabama, who planted it about 1840-1845.] (Bot.)
   A tall perennial grass (Sorghum Halepense), valuable in the
   Southern and Western States for pasture and hay. The
   rootstocks are large and juicy and are eagerly sought by
   swine. Called also Cuba grass, Means grass, Evergreen
   millet, and Arabian millet.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

millet \mil"let\ (m[i^]l"l[e^]t), n. [F., dim. of mil, L.
   milium; akin to Gr. meli`nh, AS. mil.] (Bot.)
   The name of several cereal and forage grasses which bear an
   abundance of small roundish grains. The common millets of
   Germany and Southern Europe are Panicum miliaceum, and
   Setaria Italica.

   Note:

   Arabian millet is Sorghum Halepense.

   Egyptian millet or

   East Indian millet is Penicillaria spicata.

   Indian millet is Sorghum vulgare. (See under Indian.)


   Italian millet is Setaria Italica, a coarse, rank-growing
      annual grass, valuable for fodder when cut young, and
      bearing nutritive seeds; -- called also Hungarian grass.


   Texas millet is Panicum Texanum.

   Wild millet, or

   Millet grass, is Milium effusum, a tall grass growing in
      woods.
      [1913 Webster]