1informal A siren or klaxon, especially (now historical) an air-raid siren.
2military slang A kind of mortar or rocket launcher used by German forces in the Second World War (1939–45); especially = nebelwerfer .
3informal A moaner, a complainer; a pessimist.
1940s. From moaning + Minnie, female forename, in sense 2 punningly after Minnie.