Middle of the road
Before the Civil War, most roads, including highways between major cities, were narrow and poorly maintained. The wheels of carriages and wagons tended to rut the edges. After a heavy rain, travelers walking along the roads stayed away from the sides and held to the center as much as they could. By the late 1800s, the state of America's roads had made its way into politics. Populists who wanted to avoid extreme positions on the issues of the day were called "middle of the roaders" for their cautiousness. The label is still used today for anyone who adopts a moderate stand.
According to word historian Webb Garrison, one of civilized man's first major achievements was the invention of a mechanical way to crush grain - the mill. Many of our expressions today still come from it. "To be put through the mill" means to be tested - and usually it's a grinding test. (Imagine the rough treatment a grain of wheat endures in a mill.) A less common expression is "to draw water to your own mill," meaning to take unfair advantage of a situation or person.
Finally, the circular motion of the mill wheel inspired the more common phrase "to mill about," meaning to move about in a circle in a confused and aimless way, around and around and around.
This naval wake-up call that later became "Shake a leg!" meant "Jump out of bed and be quick about it!" On 19th-century sailing vessels, the ship's crew would have to show a leg over the side of their hammocks to acknowledge that they'd heard the mate's call. Within minutes, though, their feet had better hit the deck.
This expression, meaning "neat and orderly," was first attributed to New England cooks who carefully arranged their sliced apples in rows in a pie crust. But according to scholars, the term was commonly used in England in the early 17th century, long before it began to be used in America. These scholars say its source is a corruption of the French phrase nappes-pliés, or "folded linen." Back then, dinner napkins were neatly folded after a meal and placed tidily away in a drawer. And arranged in a precise pattern just like ... apple slices in a pie.
SOURCES: 'The Barnhart Dictionary of Etymology,' by Robert Barnhart; 'The Encyclopedia of Word and Phrase Origins,' by Robert Hendrickson; 'Morris Dictionary of Word and Phrase Origins,' by W. and M. Morris; 'Why You Say It,' by Webb Garrison; 'Have a Nice Day!' by Christine Ammer, 'Brewer's Dictionary of Phrase and Fable,' by Ivor Evans; 'A Browser's Dictionary,' by John Ciardi