A Quick and Simple Dictionary

tumbleweed

1. Noun.  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. Adjective.  Describing unwonted 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.