For years, activists have worked to rid the world of nuclear weapons, while a dieter's priority might be to rid himself of ten extra pounds. Freeing someone from something unwanted is to rid them of it, whether it's ants in their kitchen or stress about their job. In the thirteenth century, rid meant "clear a space, set free, or save," from a Scandinavian root that's related to the Old Norse ryðja, "to clear land of obstructions."