mum [LME] Like ma [E19th] and mama [M16th], mum [L16th] or mom [M19th] and mummy [M18th] go back eventually to the first semi-articulate sounds made by children, which tend to be ‘ma, ma’. *Mother itself probably has the same origin. The expressions mum’s the word and to keep mum are perhaps most associated with life during the Second World War, conjuring up warnings about careless talk costing lives—for example, ‘Be like dad. Keep mum.’ Both phrases are much older, being recorded as far back as the early 16th century. The word mum itself was used on its own in medieval times to mean ‘hush!’ or ‘shh!’, and probably originated as a representation of the sound you make when you close your lips firmly together and try to speak. It also gave us mumble [ME] and mumps [L16th], a disease that makes you look as if you are making a face like someone keeping mum. Ancient Egyptian mummies are named after the substance in which the dead person’s body was embalmed. Mummy in this sense goes back to Arabic mūmiyā ‘bitumen’ for ‘the body of an embalmed person or animal’ and is recorded in English from the early 17th century.