Thalidomide is a drug. It was sold from the late 1950s as something safe and gentle — it made people calm and helped them sleep, and doctors gave it to pregnant women for morning sickness. Then it became clear that it did terrible harm. Babies whose mothers had taken it were born with arms and legs that had not grown properly, and many did not survive. Thousands of families were affected before the drug was pulled from sale in the early 1960s. Because of that, the word carries far more than its plain meaning. When people say thalidomide now, they are usually talking about the disaster, not the pill: it is the standard example of why new medicines must be tested hard and long, and why a drug that seems safe for an adult may not be safe for a baby growing inside someone. Modern drug-safety rules in most countries came partly out of it. There is one more turn to the story, and it surprises people: the drug did not disappear. Doctors found it works against certain cancers and against a serious problem caused by leprosy, so it is still used today — but under very strict control, and never for anyone who might become pregnant. It is written with a small letter, thalidomide, though you will see it capitalised as a brand name in older writing.