Dusty aggregation of plant matter rolled along the ground by the desert wind. A cliche of Western movies, emphasising silence or stillness, e.g. as the hero rides into an apparently deserted frontier town. Often used in connection with the death of a conversation after one participant unwittingly reveals that they are a moron. See also tumbleweed moment.
"But then Katie made a singularly unfunny cancer joke..."
Something to say during an uncomfortable silence or awkward pause in conversation. the conversation is so dead that a tumbleweed could be blowing through the people you are hanging out with like a desert.