(1) Forming or relating to an end or limit. (2) Fatal.

A terminal disease ends in death. If you're *terminally* bored, you're “bored to death.” For many students, a high-school diploma is their terminal degree (others finish college before *terminating* their education). A bus or train *terminal* is the endpoint of the line. A computer terminal was originally the endpoint of a line connecting to a central computer. A terminal ornament may mark the end of a building, and terminal punctuation ends this sentence.

Not precisely determined; vague.

When you *determine* something, you decide on what it is, which means you put limits or boundaries on its identity. So something indeterminate lacks identifying limits. A mutt is usually the product of indeterminate breeding, since at least the father's identity is generally a mystery. A painting of indeterminate origins is normally less valued than one with the painter's name on it. And if negotiations are left in an indeterminate state, nothing has been decided.

Having or seeming to have no end; tiresomely drawn out.

Nothing is literally endless, except maybe the universe and time itself, so *interminable* as we use it is always an exaggeration. On an unlucky day you might sit through an interminable meeting, have an interminable drive home in heavy traffic, and watch an interminable film—all in less than 24 hours.

(1) The end of a travel route (such as a rail or bus line), or the station at the end of a route. (2) An extreme point; tip.

This word comes straight from Latin. In the Roman empire, a terminus was a boundary stone, and all boundary stones had a minor god associated with them, whose name was Terminus. Terminus was a kind of keeper of the peace, since wherever there was a terminus there could be no arguments about where your property ended and your neighbor's property began. So Terminus even had his own festival, the Terminalia, when images of the god were draped with flower garlands. Today the word shows up in all kinds of places, including in the name of numerous hotels worldwide built near a city's railway terminus.

Having or relating to the Earth as the center.

The idea that the Earth is the center of the universe and that the sun revolves around it is an ancient one, probably dating back to the earliest humans. Not until 1543 did the Polish astronomer Copernicus publish his calculations proving that the Earth actually revolves around the sun, thus replacing the geocentric model with a *heliocentric* model (from *Helios*, the Greek god of the sun). But *geocentrism* remains central to various religious sects around the world, and still today one in five adult Americans believes the sun revolves around the Earth.

The science that deals with the physical processes and phenomena occurring especially in the Earth and in its vicinity.

Geophysics applies the principles of physics to the study of the Earth. It deals with such things as the movement of the Earth's crust and the temperatures of its interior. Another subject is the behavior of the still-mysterious *geomagnetic* field. Some *geophysicists* seek out deposits of ores or petroleum; others specialize in earthquakes; still others study the water beneath the Earth's surface, where it collects and how it flows.

We don't give much thought to geostationary satellites, but many of us rely on them daily. Anyone who watches satellite TV or listens to satellite radio is dependent on them; the weather photos you see on TV are taken from geostationary satellites; and military information gathering via satellite goes on quietly day after day. (Though the satellites that provide GPS service for your car or cell phone actually aren't geostationary, since they orbit the Earth twice a day.) By 2009 there were about 300 geostationary satellites in operation, all of them moving at an altitude of about 22,000 miles. Since they hover above the same spot on Earth, your receiving dish or antenna doesn't have to turn in order to track them.

Of, relating to, or using the natural heat produced inside the Earth.

*Geothermal* comes partly from the Greek *thermos*, “hot” (see THERM/THERMO). Most geothermal electricity is provided by power plants situated in areas where there is significant activity of the Earth's great tectonic plates—often the same areas where volcanoes are found. But hot water from deep underground may be used by cities far from volcanoes to heat buildings or sidewalks. And a newer source of geothermal energy relies on a less dramatic kind of heat: Individual homeowners can now install heat pumps that take advantage of the 50°-60° temperature of the soil near the surface to provide heating in cold weather (and air-conditioning in the warm months). These very small-scale geothermal systems may eventually supply more useful energy than the large power plants.