The Collaborative International Dictionary of English v.0.48:

Tumbleweed \Tum"ble*weed`\, n. (Bot.)
   Any plant which habitually breaks away from its roots in the
   autumn, and is driven by the wind, as a light, rolling mass,
   over the fields and prairies; such as witch grass, wild
   indigo, Amarantus albus, etc.
   [1913 Webster]