"Mum's the word" has been a popular expression since at least the 17th century;
"Seal up your lips, and give no words but mum." - Shakespeare, Henry VI,
Part II, I, ii.
Mum, with the meaning of silent, is thought to originate in Middle English - the name linguists give to the diverse forms of the English language spoken in England between the Norman invasion in 1066 and about 1470.
The OED defines 'mum' as an inarticulate sound made with closed lips.
Kenn Nesbitt is new Children's Poet Laureate(Jun 12 2013) Kenn Nesbitt has been named the new Children's Poet Laureate: Consultant in Children's Poetry to the Poetry Foundation, which noted that the two-year position...