The Collaborative International Dictionary of English v.0.48:

Ray grass \Ray" grass`\ (r[=a]" gr[.a]s`). [Etymol. of ray is
   uncertain.] (Bot.)
   A perennial European grass (Lolium perenne); -- called also
   rye grass, and red darnel. See Darnel, and Grass.
   [1913 Webster]

   Italian ray grass or Italian rye grass. See Darnel, and
      Grass.
      [1913 Webster]