Real Dictionary

tumbleweed
uncountable noun: Tumbleweed is a plant that grows in desert areas in North America. It breaks off from its roots at the end of its life and then blows around on the ground.

tumbleweed in American English
any of a number of plants, as the pigweed or Russian thistle, that break off near the ground in autumn and are blown about by the wind
noun: any of various plants, as Amaranthus albus, A. graecizans, or the Russian thistle, Salsola kali, whose branching upper parts become detached from the roots and are driven about by the wind

tumbleweed in British English
noun: any densely branched plant that breaks off near the ground on withering and is rolled about by the wind, esp one of several amaranths of the western US and Australia