The Collaborative International Dictionary of English v.0.48:

Doob grass \Doob" grass`\ [Hind. d?b.] (Bot.)
   A perennial, creeping grass (Cynodon dactylon), highly
   prized, in Hindostan, as food for cattle, and acclimated in
   the United States. [Written also doub grass.]
   [1913 Webster]