A painkiller is a medicine that reduces pain or takes it away for a while. You take it for a headache, a sore tooth, period pain, or after you hurt yourself. Some kinds are mild and sold in a pharmacy; some are strong and only a doctor can give them. The everyday English word is painkiller; it names the whole shelf, not one box. In Taiwan, people often reach for a brand name when they mean a common tablet — 普拿疼 is the one you hear for that white paracetamol pill. Mainland Chinese often says 撲熱息痛 for that same drug; here the household word is the brand. Though actually, killer here does not mean a bad person. It only means “something that kills the pain.” A painkiller does not always kill the cause of the pain; it turns the hurt down so you can get through the day. It is also not the medicine that puts you to sleep for an operation.