Here are a few of my favorite entries, all beginning with the letter “E," from Word and Phrase Origins, a thoroughly delightful book published in 1997.
Edelweiss. A white flower found high in the Alps (and perhaps best known to Americans through the song of the same name in "The Sound of Music"), the edelweiss takes its name from two German words---edel, meaning noble and weiss, meaning white.
Egregious. The word egregious is derived from the Latin ex gregis (meaning "out of the flock"). For 300 years, until the mid 19th century, egregious meant outstandingly good or outstandingly bad. Since then, it has meant only outstandingly bad. No one knows why the meaning became more limited.
Epsom salts. Crystals of hydrated magnesium sulfate were discovered in a mineral spring in Epsom, England (a town about 15 miles from central London) in the late 17th century. Epsom salts, now used as a health and beauty aid, are commercially produced by dissolving magnesium carbonate in sulfuric acid.
Euchre. Euchre, a card game popular in the early 19th century American West, also means to cheat or swindle. Cheating was so prevalent during the playing of the game that its name became synonymous with the chicanery.
Even keel. The expression to get things on an even keel, meaning to make things move smoothly, derives from the nautical term even keel, which one early 19th century writer defined as a ship which "draws the same quantity of water abaft as forward."
A note about the author: Word and Phrase Origins was written by Robert Hendrickson, now 85 years old and the author of more than 25 other books, including American Literary Anecdotes, New York Tawk, and More Cunning than Man: A Social History of Rats and Men.