(1) Thick or murky, especially with churned-up sediment. (2) Unclear, confused, muddled.

The Colorado River in spring, swollen by melting snow from the high mountains, races through the Grand Canyon, turbid and churning. A chemical solution may be described as turbid rather than clear. And your emotions may be turbid as well, especially where love is involved: What did he mean by that glance? Why did she say it like that?

To upset, confuse, or disarrange.

With its *per-* prefix, *perturb* meant originally “thoroughly upset,” though today the word has lost most of its intense edge. *Perturb* and *perturbation* are often used by scientists, usually when speaking of a change in their data indicating that something has affected some normal process. When someone is referred to as *imperturbable*, it means he or she manages to remain calm through the most trying experiences.

The oldest and simplest form of turbine is the waterwheel, which is made to rotate by water falling across its blades and into buckets suspended from them. Hero of Alexandria invented the first steam-driven turbine in the 1st century A.D., but a commercially practical steam turbine wasn't developed until 1884; steam turbines are now the main elements of electric power stations. Jet engines are gas turbines. A *turbojet* engine uses a turbine to compress the incoming air that feeds the engine before being ejected to push the plane forward; a *turboprop* engine uses its exhaust to drive a turbine that spins a propeller. A wind turbine generates electricity by being turned by the wind; the largest now have vanes with a turning diameter of over 400 feet.

(1) Stirred up, agitated. (2) Stirring up unrest, violence, or disturbance.

Some people lead turbulent lives, and some are constantly in the grip of turbulent emotions. The late 1960s are remembered as turbulent years of social revolution in America and Europe. Often the captain of an airplane will warn passengers to fasten their seatbelts because of upper-air *turbulence,* which can make for a bumpy ride. El Niño, a seasonal current of warm water in the Pacific Ocean, may create turbulence in the winds across the United States, affecting patterns of rainfall and temperature as well.

Speaking readily and rapidly; talkative.

A voluble person has words “rolling” off his or her tongue. In O. Henry's famous story “The Ransom of Red Chief,” the kidnappers nab a boy who turns out to be so unbearably voluble that they can hardly wait to turn him loose again.

(1) To pass (responsibility, power, etc.) from one person or group to another person or group at a lower level of authority. (2) To gradually go from an advanced state to a less advanced state.

With its *de-* prefix, *devolution* implies moving backward. Once powers have been centralized in a unified government, giving any powers back—that is, devolving the power—to a smaller governmental unit can seem to be reversing a natural development. In a somewhat similar way, a job that your boss doesn't want to do may devolve upon you. But *devolve* and *devolution* are also treated nowadays as the opposites of *evolve* and *evolution*. So we may also speak of moral devolution, such as occurred in Germany in the 1930s, when a country with an extraordinary culture became a brutal dictatorship. And parents may watch their slacker teenager and wonder if devolution is occurring right in front of their eyes.

A process of change from a lower, simpler, or worse state to one that is higher, more complex, or better.

Part of the humor of the old *Flintstones* cartoon show is that it contradicts what is known about biological evolution, since humans actually *evolved* long after dinosaurs were extinct. *Evolution* can also be used more broadly to refer to technology, society, and other human creations. For example, an idea may evolve, even in your own mind, as the months or years pass. And though many people don't believe that human beings truly become better with the passing centuries, many will argue that our societies tend to evolve, producing more goods and providing more protection for more people.

(1) Having a pattern of curved windings. (2) Involved, intricate.

*Convolution* originally meant a complex winding pattern such as those visible on the surface of the brain. So a convoluted argument or a convoluted explanation is one that winds this way and that. An official document may have to wind its way through a convoluted process and be stamped by eight people before being approved. Convoluted language makes many people suspicious; as a great philosopher once said, “Anything that can be said can be said clearly.”