To come together to form one group or mass.

Social movements are often said to coalesce when groups with somewhat different interests realize how much they have in common. Some physicists believe that planets coalesced not from space rocks but from icy clouds of cosmic dust. Some people even study how languages coalesce—for example, the fairly new language Afrikaans, a mixture of Dutch and native languages spoken in South Africa, which only really solidified about 150 years ago.

Cogeneration is basically the production of energy and usable heat (generally in the form of steam and hot water) in the same plant, usually by capturing heat that in older plants used to be simply wasted. It's one of the principal ways in which countries intend to reduce their greenhouse-gas emissions so as to slow climate change. Cogeneration plants are often small, and the fuels used in them are varied. Lumber mills, for instance, can operate their own cogeneration plants, feeding them with wood scraps and sawdust, and wastewater treatment plants generate gas that can likewise be used as a source of energy. Since it's hard to move heat long distances, cogeneration is most efficient when the heat can be used nearby. Though the general public today knows little about cogeneration, more and more of us will be benefiting from it in the coming years.

Dependency on addictive substances has been known for centuries, but the concept of codependency got its name only as recently as 1979. For many of us, codependency isn't easy to understand; we may keep asking “Why doesn't she just leave him?” and find it hard to accept the answers we get. *Codependents* usually don't share their partners' addiction, but their lives tend to be taken over with the burden of caring for and protecting the spouse or partner. In recent years, people have started claiming that all kinds of conditions—anorexia, overeating, gambling, fear of intimacy, etc.—can result in codependency. Many experts think all of this has gone too far; still, almost everyone agrees that spouses of alcoholics and drug addicts face unique difficulties and should look for support and advice anywhere they can find it.

(1) The action or state of sticking together. (2) Molecular attraction by which the particles of a body are united throughout the mass.

*Cohesion* is one of the noun forms of *cohere*; the others are *cohesiveness* and *coherence*, each of which has a slightly different meaning. *Coherence* is often used to describe a person's speech or writing. An *incoherent* talk or blog post is one that doesn't “hang together” ; and if the police pick up someone who they describe as *incoherent*, it means he or she isn't making sense. But to describe a group or team that always sticks together, you would use *cohesive*, not *coherent*. And the words you'd use in Chemistry class to describe the way molecules hang together—for example, the way water forms into beads and drops—are *cohesion, cohesive,* and *cohesiveness*.

The way in which words are put together to form phrases, clauses, or sentences.

Syntax is basically about what word comes before and after another word; in other words, it's part of the larger subject of grammar. Syntax is often an issue in poetry, and it's usually discussed in connection with *diction*—that is, the poet's choice of words. So, for example, your English professor might point out the *syntactic* difference between “Whose woods these are I think I know” and “I think I know whose woods these are” ; whereas if the discussion was about diction instead, the question might be about the choice of “woods” rather than “land,” or “think” rather than “bet.”

To make something by combining different things.

*Synthesize* is a very common word in chemistry, since chemists are constantly synthesizing new compounds—that is, *synthetic* compounds— including drugs and industrial chemicals. It's also often used when talking about writing; nonfiction writers must often synthesize large amounts of material from many sources to produce a book—which represents a *synthesis* of the important materials. An electronic *synthesizer*creates new sounds (which may imitate the sounds of acoustic instruments) by generating different basic tones and then manipulating and merging them together with others.

The increased effectiveness that results when two or more people or businesses work together.

An old saying, “The whole is greater than the sum of its parts,” expresses the basic meaning of *synergy*. The word is sometimes used in a purely physical sense, especially when talking about drugs; sometimes a “cocktail” of drugs may be more effective than the sum of the effectiveness of each of the separate drugs. But the word is best known in the world of business. The notion that, when the right two companies merge, they'll produce a profitable synergy seemed exciting in the 1990s, when *synergy* became a trendy buzzword (even though it's actually been around since the 17th century). The idea of synergy was one factor in what became a “merger mania” ; unfortunately, business synergy often turned out to be harder to achieve than to imagine.

A group of signs and symptoms that occur together and characterize a particular abnormality or condition.

Combining its two Greek roots, *syndrome* means basically “running together.” So when diagnosing a condition or disease, doctors tend to look for a group of symptoms existing together. As long as a set of symptoms remains mysterious, it may be referred to as a specific syndrome. But if that name is used for a while, it may become the condition's permanent name, even after an underlying cause has been found. So today we have *Down syndrome, acquired immune deficiency syndrome, Asperger 's syndrome, carpal tunnel syndrome, chronic fatigue syndrome, Tourette 's syndrome, sick building syndrome,* and many more. And since mental conditions often turn out to have physical causes, *syndrome* is used in psychology as well as in medicine.