A long-lost person or thing is one you have not seen for a long time — often so long that meeting them again, or finding the thing again, feels like a small surprise. A long-lost friend is not just an old friend you still message. You lost touch. Years went by. You may even have wondered if you would ever see them again. Families use it the same way: a long-lost cousin, a long-lost brother. You can also put it in front of objects: a long-lost letter, a long-lost photograph, a long-lost key — something that went missing and then turned up. There is a little story-feeling in the word, warmer and more dramatic than missing or old. People sometimes stretch it for effect, even when the two people were never that close, because the phrase paints a picture. It almost always takes a hyphen, and it almost always sits in front of a noun. It does not mean the person has died. It means they have been out of your life for a long time.