tumbleweed

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of various densely branched annual plants, such as amaranth and Russian thistle, that break off from the roots at the end of the growing season and are rolled about by the wind.

Century Dictionary and Cyclopedia

1. n. A branching plant whose top assumes a globular figure and in autumn is detached and rolled over the plains by the wind, scattering its seed. The name is given to several such plants in the western United States. Species so called are Amarantus albus (compare ghost-plant) and A. blitoides, Psoralea lanceolata (Dakota and Montana), the bug-seed, Corispermum hyssopifolium, and the winged pigweed, Cycloloma platyphylla. Also called rolling-weed.

Wiktionary

1. n. 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; as witch grass, wild indigo, Amaranthus albus, etc.
2. adj. Describing unwanted silence and inactivity. Often used of a situation when one makes a statement that is ignored or ill-received from one’s audience. Gives the impression that a tumbleweed has passed through the room, as the resultant silence is likened to that of a desolate desert.

GNU Webster's 1913

1. 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.

WordNet 3.0

1. n. prickly bushy Eurasian plant; a troublesome weed in central and western United States
2. n. any plant that breaks away from its roots in autumn and is driven by the wind as a light rolling mass
3. n. bushy plant of western United States
4. n. bushy annual weed of central North America having greenish flowers and winged seeds