Q From Tim Marsh in Australia: Can you shed any light on the origin of the phrase to keep mum? I found, much to my delight, the following headline on the Web site for Melbourne’s The Age newspaper: ‘Presidential candidate Bush keeps mum on cocaine’.
A I hope the dear lady appreciates his efforts.
The word mum is one of the few that we can say for certain are onomatopoeic, which imitate or echo some sound. The sound in this case is the inarticulate murmur ‘mmmmm’, the only noise one can make when one’s mouth is kept firmly shut. The word has been recorded in English from the fourteenth century in various spellings but settled to its modern form in the sixteenth century.
It has produced several compounds, including mummer (a mime actor, one who performs silently, though the word is also linked to the French momeur), the verb to mumble and, less obviously, the name of that nasty disease mumps. This may derive from mump, an obsolete word for a grimace, which could possibly refer to the altered shape of the face due to the swollen glands in the neck, or perhaps to a resulting difficulty in speaking. It’s the same word as the old verb to mump meaning to sulk. (Neither is connected with mumping in the sense of begging, which comes from a different word, Dutch in origin, or of mum for a type of beer, whose origin is uncertain.) And there are the various phrases, like mum’s the word and your to keep mum which also include the idea of keeping silent.
The sense of mum that produced the delightful double meaning in the headline you spotted is very much more modern. As a shorted form of mummy it appears only at the start of the nineteenth century. Until then, there would have been no joke, nor would that poster slogan of the Second World War have been possible, the one that enjoined people not to talk carelessly to strangers: “Be like Dad: keep Mum”.