People often use the word *average* without realizing that there are two common forms of average. Suppose you want to find the average net worth of a group of people—that is, the average value of everything they possess. To find one type of average, called the *mean*, you'd simply add up the total value of money and property of everyone in the group and divide it by the number of people. To find the other type, called the *median,* you'd identify the net worth of the person who is richer than half the people and poorer than the other half. So if Warren Buffett drove through a tiny village in India, the mean net worth of those in the village would suddenly rise to perhaps a billion dollars, but their median net worth would remain close to zero. Which figure would be more meaningful?

(1) To work with opposing sides in an argument or dispute in order to get an agreement. (2) To achieve a settlement or agreement by working with the opposing sides.

*Mediation* is often used in disputes between companies and labor unions, and the government actually provides *mediators* for such disagreements. The mediator tries to bring the two sides to an agreement, but doesn't have the power to actually order such an agreement. Mediators also sometimes have a role in international disputes; when two neighboring countries claim exclusive fishing rights in the same ocean waters, for example, they may invite a trained mediator to help settle the argument. *Arbitration* is similar to mediation, but in arbitration both parties in a dispute agree to accept the arbitrator's decision.

A person who works with opposing sides in a dispute in order to bring about an agreement.

Since *inter-* means “between, among,” an intermediary is someone who moves back and forth in the middle area between two sides—a “go-between.” *Mediator* (which shares the *medi-* root) is often a synonym, and so is *facilitator*; *broker* and *agent* are often others. Thus, a real-estate broker or agent shuttles between a house's buyer and seller, who may never even meet each other. Financial *intermediation* is what happens when you put money in a bank or investment firm, which then invests it in various companies; if you want, you can instead cut out the intermediary and invest the money directly in companies of your own choosing.

The quality of being not very good.

People interested in words always point out that *mediocrity* doesn't mean quite what its main root would indicate: Why doesn't it describe something that's right in the middle of the pack, exactly what you would expect? Instead the words *mediocrity* and *mediocre* always suggest disappointment. A mediocre play is one you wish you hadn't wasted an evening on, and the mediocre actor in it should probably find another profession. A person can even be called a mediocrity, though it isn't very nice and you'd never do it to his face.

In geometry, a shape with four sides where only the opposite sides and angles are equal.

Rhomboids, like triangles, may take various different shapes, but they always look like a lopsided diamond or rectangle. As both a noun and an adjective, *rhomboid* can be applied to anything with those shapes, such as certain muscles of the upper back when viewed from behind. Whenever you hear about rhomboid exercises, rhomboid strain, or rhomboid pain, it involves those muscles, which attach your shoulder blades to your spine and can be strained by carrying a heavy backpack, serving a tennis ball, or just slumping in your chair in front of a computer all day.

A large muscle of the shoulder.

The fourth letter of the Greek alphabet is *delta*, and a capital delta is triangle- shaped. In English, *delta* commonly means the sand deposits that form a huge triangle at the mouth of certain large rivers. *Deltoid* as an adjective means “having a triangular shape,” and botanists often use the word to describe the shape of certain leaves. The triangular, swept-back wings seen on jet fighter aircraft are called *delta wings*. Your deltoid muscles—not far from your rhomboids—form a cap on your shoulders, and some gym trainers even treat *shoulder* and *deltoid* as synonyms. Can you guess the general shape of deltoids when seen from the side?

Resembling a tree in form.

*Dendrology* is the study of trees, and those who do the studying are called *dendrologists*. So *dendroid* describes something that “branches” in all directions from a central “trunk” in an irregular way. The word is almost always used by biologists, who often speak of dendroid seaweeds, dendroid moss, and dendroid algae.

Looking or acting like a human.

A humanoid robot, sometimes called an *android*, is a robot that resembles a human. Accounts of the yeti, Sasquatch, and Bigfoot continue to fascinate us mainly because of their humanoid characteristics. The idea of creating a monstrous *humanoid*, such as the Jewish golem or Victor Frankenstein's creation, has intrigued us for centuries. “Humanoid Animation” is a standard for creating humanlike figures for video that lets the same figure be used in a variety of 3-D games—some of which have nothing but humanoids for characters.