A dry, round, dead-looking plant that grows in the dry open country of the western United States. When it dies, the top part breaks off from the root and the wind rolls it across the ground — that rolling is where the name comes from. It is a real plant, but for most people the word is mainly a picture: an empty desert road, a dusty town, one dry ball of plant blowing past. Cowboy films used it so much that it became a symbol of emptiness and of nowhere. That gave the word a second, joking life in modern English. If someone tells a joke and no one laughs, English speakers say 'tumbleweed' — meaning the silence was as empty as a desert street. You will see this a lot online. It can be a countable noun ('a tumbleweed rolled past') or uncountable when you mean the stuff in general ('the fence was full of tumbleweed').