The Collaborative International Dictionary of English v.0.48:

Burgrass \Bur"grass`\, n. (Bot.)
   Grass of the genus Cenchrus, growing in sand, and having
   burs for fruit.
   [1913 Webster]

WordNet (r) 3.0 (2006):

burgrass
    n 1: a grass of the genus Cenchrus [syn: burgrass, bur
         grass]