At times a writer may need to go further than a brief sentence definition and provide readers with a fuller, extended definition, as in the following example:

People often refer to being “hooked on TV.” Does this, too, fall into the light-hearted category of cookie eating and other pleasures that people pursue with unusual intensity, or is there a kind of televison viewing that falls into the more serious category of destructive addiction?. . .

Let us consider television viewing in the light of the conditions that define serious addictions.

Not unlike drugs or alcohol, the television experience allows the participant to blot out the real world and enter into a pleasurable and passive mental state. The worries and anxieties of reality are as effectively deferred by becoming absorbed in a television program as by going on a “trip” induced by drugs or alcohol. And just as alcoholics are only inchoately aware of their addiction, feeling that they control their drinking more than they really do (“I can cut it out any time I want—I just like to have three or four drinks before dinner”), people similarly overestimate their control over television watching. Even as they put off other activities to spend hour after hour watching television, they feel they could easily resume living in a different, less passive style. But somehow or other while the television set is present in their homes, the click doesn’t sound. With television pleasures available, those other experiences seem less attractive, more difficult somehow. . . .

The self-confessed television addict often feels he “ought” to do other things—but the fact that he doesn’t read and doesn’t plant his garden or sew or crochet or play games or have conversations means that those activities are no longer as desirable as television viewing. In a way a heavy viewer’s life is as imbalanced by his television “habit” as a drug addict’s or an alcoholic’s. He is living in a holding pattern, as it were, passing up the activities that lead to growth or development or a sense of accomplishment. This is one reason people talk about their television viewing so ruefully, so apologetically. They are aware that it is an unproductive experience, that almost any other endeavor is more worthwhile by any human measure.

Finally, it is the adverse effect of television viewing on the lives of so many people that defines it as a serious addiction. The television habit distorts the sense of time. It renders other experiences vague and curiously unreal while taking on a greater reality for itself. It weakens relationships by reducing and sometimes eliminating normal opportunities for talking, for communicating.

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And yet television does not satisfy, else why would the viewer continue to watch hour after hour, day after day? “The measure of health,” writes Lawrence Kubie, “is flexibility . . . and especially the freedom to cease when sated.” But the television viewer can never be sated with his television experiences—they do not provide the true nourishment that satiation requires—and thus he finds that he cannot stop watching.

— MARIE WINN, “TV Addiction”

In this example, Marie Winn offers an extended definition of television addiction that begins with a comparison. Comparison or contrast is often the most effective way to present an unfamiliar term or concept to readers. The key is to know your readers well enough to find a term nearly all of them will know to compare to the unfamiliar term.

Extended definitions may also include negative definitions—explanations of what the thing being defined is not:

It’s important to be clear about the reverse definition, as well: what dinosaurs are not. Dinosaurs are not lizards, and vice versa. Lizards are scaly reptiles of an ancient bloodline. The oldest lizards antedate the earliest dinosaurs by a full thirty million years. A few large lizards, such as the man-eating Komodo dragon, have been called “relics of the dinosaur age,” but this phrase is historically incorrect. No lizard ever evolved the birdlike characteristics peculiar to each and every dinosaur. A big lizard never resembled a small dinosaur except for a few inconsequential details of the teeth. Lizards never walked with the erect, long-striding gait that distinguishes the dinosaur like ground birds today or the birdlike dinosaurs of the Mesozoic.

— ROBERT T. BAKKER, The Dinosaur Heresies