A lesion is damage to a part of the body. It may be on the skin, where you can see a sore or a mark, or it may be inside — in the stomach, the liver, or the brain — where only a doctor with a scan can find it. Illness can cause it, and so can an injury. Doctors like the word because it is wide: it does not say whether the damage is a cut, a lump, a dying patch of tissue, or something else; it only says this bit is not as it should be. Ordinary people more often say wound, cut, sore, or scar when they can see it. You will hear lesion mainly in hospitals, in medical news, and in science. It is a fairly formal, technical noun. It came into English from Middle English lesioun, from Old French lesion, from Latin laesiō (hurt, harm, injury), from laesus, the past form of laedō, to strike or hurt.