The name does two jobs at once. It says the person complains, and it says the complaining goes on and on, in the long low sound that moan describes. It is light rather than heavy: people use it to tease a friend, or to tell someone to stop and cheer up. Because it is a name, it usually appears with be: he is a moaning Minnie, do not be such a moaning Minnie. It can be used about a man as easily as about a woman. Said straight to someone's face it can still sting, because it labels the person and not just the complaint.

Again the name is about sound, not about size or power. The rockets were known for the long screaming noise they made on the way, and soldiers gave that noise a person's name. This is a historical term: you will meet it in war memoirs, documentaries and museum labels. It shares its name with the air-raid siren for the same reason, because both of them wailed.

The name comes from the sound. A siren does not stop in one note; it slides up and down for a long time, which is close to what English calls a moan. People who lived through those years used the name the way you would use a nickname for a thing you heard every week. You will meet it today mostly in history writing, in museums, and in older people's memories, not in ordinary conversation.