Subsidence is what we call it when the ground itself sinks — not a sudden hole, usually, but the slow settling of land to a lower level than the land around it. It happens for real reasons a student can picture: too much water pumped out from under the ground, old mine tunnels collapsing, soft soil drying and shrinking, heavy buildings pressing down over many years. In Taiwan this word matters. Parts of Yunlin and Changhua have sunk metres over decades because of groundwater pumping for fish farms and farming, and this is exactly the word English news uses for it: land subsidence. The word has a second, narrower home in Britain, where it is a house word. If a British house has 'subsidence', it means the ground under one part of the house has sunk and the walls have cracked. It is the thing house buyers fear and insurance companies argue about; a British person can say 'the house has subsidence' the way we might say a house has termites. Grammatically it is uncountable — we say 'subsidence', not 'a subsidence' or 'subsidences', in almost every normal case. It is a technical and news word rather than a chatting word; the ordinary way to say it is 'the ground is sinking'.