Source : Webster's Revised Unabridged Dictionary (1913)

Panic \Pan"ic\, n. [L. panicum.] (Bot.)
   A plant of the genus {Panicum}; panic grass; also, the edible
   grain of some species of panic grass.

   {Panic grass} (Bot.), any grass of the genus {Panicum}.

Source : WordNet®

panic grass
     n : any grass of the genus Panicum; grown for grain and fodder