[mum] adj [prob. imit. of a sound made with closed lips] (14c): silent "keep ~"
[2]mum vi mummed ; mum.ming [ME mommen, fr. MF momer to go masked] (1530) 1: to perform in a pantomime
2: to go about merrymaking in disguise during festivals [3]mum n [G Mumme] (1640): a strong ale or beer [4]mum chiefly Brit var of mom [5]mum n (1917): chrysanthemum