A sadist is a person who enjoys hurting other people, or making them suffer. The hurt can be of the body, or of the feelings — saying cruel things on purpose, for example. In serious talk, this is a dark word: someone who really gets pleasure from another person’s pain. Though actually, people also use it loosely, almost as a joke: “You’re a sadist!” when a teacher gives too much homework, or a coach makes the team run again. That stretch is common, but it is milder than the full meaning. The word comes from the Marquis de Sade, a French writer from a long time ago, whose stories were full of cruelty. You do not need his name to use the word, but that is where it started. It is a strong label; calling someone a sadist in earnest is an accusation, not a light remark.