keep mum - Mum is the sound a person makes by speaking without opening his or her lips: mumbling, in other words. To "keep mum," in early English usage, therefore mean something like "don't give any details," rather than "speak unintelligibly." The sense changed over time to mean "keep silent," as in the parallel expression "mum's the word."
blush - When our faces redden in shame owing to some gaffe real or imagined, we often feel as if were were on fire: the skin prickles, the pores open, the perspiration flows. Though the origins of the term as obscure, "blush" probably derives from the Old-Germanic blisan, the ancestor of our word "blaze."
tapioca - A gummy starch that is obtained from the root of the cassava plant, which is native to South America. The name comes from the Portuguese pronunciation of a Tupi Indian phrase that means "the juice from a removed heart."
toady - In early England, where toads were thought to be poisonous, traveling quack-medicine salesmen employed assistants called "toadeaters" who would pretend to eat an unfortunate amphibian and then to get better once they'd had a swig of the salesman's magical elixir. The word "toady," meaning an unthinking henchman, turns up as an abbreviation of "toadeater" in about 1690.