shake, sweep away

蕩 is composed of the radical 艸 (grass) and 湯 (hot water). 湯 refers to boiling water, which churns and moves constantly when boiling, resembling wild grass swaying in a strong wind. Additionally, places scalded by boiling water become barren, with no grass growing, so 蕩 not only means shaking or swaying but also carries the meaning of sweeping away or clearing.