The Strangest of Idioms...Seal Up Your Lips and Say Nothing...Mums the Word
"Mum" was actually a word back in the 14th century, originating from the "mmm" humming sound one makes with a closed mouth. Thus, "mum" referred to someone unwilling or unable to speak. But the term wasn't just an old English word, it was also an old English Christmas tradition. In the Middle Ages,... Sign in to see full entry.