A very big change that shakes things up and causes trouble and difficulty while it happens. Political upheaval, social upheaval, economic upheaval — a country changing government by force, a company reorganising and firing half its staff, a family moving to a new country. The word says two things at once: the change is huge, and it is uncomfortable to live through. Use it when normal life stops working the way it used to. A war, a revolution, a financial crash, a divorce — all upheavals. A new haircut is not, however dramatic it feels. The word does not necessarily mean the change is bad in the end; historians will write about the upheaval of the industrial revolution without meaning it should not have happened. But it always means the period itself was hard and unsettled. It works both as a countable noun ("a period of great upheaval", "the upheavals of the last century") and uncountable ("a time of upheaval"). It is a fairly formal word — you meet it in news, history books, and serious writing more than in conversation, though an educated speaker will use it about their own life: "It's been a year of upheaval for us." There is also an older, literal geology meaning — rock pushed up from below by pressure in the earth — but you will rarely meet it, and the big-change meaning is the one that matters.

劇變、動盪（通常伴隨混亂與不安）