The ‘mum’ of the phrase refers to the humming sound made with a closed mouth, representing an inability or unwillingness to speak. As a word, it can be written as ‘hum’ or ‘mmm’, and it has a long history in the English language, dating all the way back to the influential Middle English poem Piers Plowman, written by William Langland in the 14th century.
To get from Piers Plowman to our modern English phrase, we have to go via the old English tradition of mummers’ plays. There aren’t any remaining texts of mumming, but they would have been a boisterous blend of panto, dancing and carol singing, performed by a bizarre cast of costumed characters. In early mumming, the cast would dance or play games in silence – which is where we get ‘miming’ from – and began to popularise the idea of ‘mum’ being linked to keeping quiet.
The actual phrase, however, didn’t come from mummers but was possibly first used, in some form, in John Palsgrave’s 1540 translation of a Latin text. He used the expression ‘mum is counsel’ In his work, The Comedye of Acolastus, he used the similar expression, ‘mum is counsel’:
“I dare not do so moche as put my hande to my mouthe, and saye mum, is counseyle.”
Inevitably, any phrase with a Tudor origin is going to appear in Shakespeare. The phrase entered the vernacular thanks in no small part to Henry VI, Part 2 and the line: “Seal up your lips and give no words but mum.”
So next time someone’s mystified about why ‘mum’s the word’, you won’t have to keep quiet about the explanation.