With the news pages and airwaves filled lately with reports of a possible "pandemic" of bird flu, some people are turning to their dictionaries for clarity on the distinction between "pandemic" and "epidemic."

Some dictionaries seem to make the distinction as clear as mud.

"Pandemic" comes from Greek roots, "pan," meaning "all" or "total" (as a panoply is a complete suit of armor) and "demos," meaning "people." "Pandemic" means, most originally and literally "of all the people." It's become a bearer of bad tidings because it's now used almost exclusively as a short form of "pandemic disease" - meaning one that breaks out seemingly everywhere all at once, affecting "all the people."

The Spanish influenza of 1918 is an oft-cited example. It's thought to have been called this not because it originated in Spain but because Spain, as a neutral party during World War I, wasn't censoring its news media at the time and so was the first major country to report on the outbreak. The Spanish themselves, meanwhile, reportedly referred to the disease as "the French flu."

The Oxford English Dictionary defines "pandemic" first as "general, universal," and then gives a second sense: "Of vulgar or sensual love." It cites a line from the English poet Shelley: "That Pandemic lover who loves the body rather than the soul is worthless."

Meanwhile, back at the department of public health, "epidemic" is being used to describe an outbreak of disease among many people in a given place within a given time period. One way to think of it is that "epidemic" is local, and "pandemic" is global.

There's a third element of this discussion, "endemic," used as an adjective and much less often as a noun, to refer to diseases considered regularly present in a community but "generally under control," as my Webster's has it. The "en" prefix means "in" – an endemic disease is one "in the people." If "pandemic" and "epidemic" recur to acute episodes, where "everyone" seems to be getting sick, "endemic" refers to chronic conditions of public health. "Endemic" also has a more benign meaning, similar to "indigenous" or "native" – certain plants or animals may be said to be "endemic" to a given place.

Of these three, "epidemic" may be the one most commonly used, but it's the one I find hardest to get a grip on. It's because of that quirky "epi" prefix, common enough in words of Greek derivation, but not easily explained in English with a single term.

"Upon" is one rendering for "epi." It seems to suggest that which is on top of something else. An epidemic might thus seen as something "upon the people," that is, prevalent, or "visited upon" the people. "Epigraphy" ("writing upon [buildings]), for instance, is a fancy term for inscriptions collectively, or their study.

Another "epi" is the "epicycle." In the complexities of Ptolemaic astronomy, charts of the heavens showed cycles and epicycles, orbits within orbits, as stargazers invented ever more complex explanations for the movements of the planets, before it was understood that they revolve around the sun, not the earth.

And for a brief moment when I was in the fourth or fifth grade, it seemed the height of sophisticated humor for some kids in class to tease the less well read by taunting, "Your epidermis is showing" – the epidermis being the normally visible outer layer of the skin.

There's another "epi" much in the news in the case of earthquakes, which is "epicenter." An epicenter is not the exact place where an earthquake occurs, which is generally below the surface. Rather it's the area of the earth's surface directly above that place.

Some people, though, use "epicenter" as if it were an intensified form of "center": the "epicenter of the new media revolution," for instance, as one online guru has it.

So, too, "penultimate," the one before the last, is sometimes used to mean "beyond the ultimate," whatever that would mean. But the "pen" particle is from Latin meaning "almost," as in peninsula ("almost island"). Evidently what's being sought here, though, is a term for "the truly extraordinary."

The lessons here? Words have meanings. Fancy particles from Greek or Latin need to be handled with care. Otherwise verbal confusion may become pandemic.

At this point, the fall foliage season around Boston is still largely in our heads.

Normally we think of the colors of autumn as hitting their peak around Columbus Day. (Wasn’t it convenient for New England’s tourism business that Christopher discovered the New World on the second Monday in October of 1492? That ensured that the commemorative federal holiday would fall in a way that gives people an extra day off to go leaf-peeping.)

But this year, continuing warm weather and what has seemed like about three weeks of drenching rain have the color calendar running somewhat late.

Unable to mobilize a real foliage expedition, I’ve been thinking about how the trees decide to let go of their leaves, and what lessons may be learned from this.

To decide is, etymologically speaking, to cut off. In this literal-minded sense, deciding is more negative than positive; it's about what one turns away from rather than turns toward.

"Two roads diverged in a yellow wood," the familiar poem by Robert Frost begins. Note that it's autumn, and at a point in the year when the leaves have actually turned.

The poem doesn't include the word "decide" in any of its forms, but the concept is there implicitly. And the poet acknowledges that choosing "the road less traveled by" will almost surely preclude – cut off, we might say – the option of the other road.

Oh, I kept the first for another day!
Yet knowing how way leads on to way,
I doubted if I should ever come back.

It's a little sad, isn't it? And yet we must decide, and let go of the options that aren't right, or are no longer right. We progress through life continually exchanging the many things possible for the single thing fully realized.

This may be especially true of creative processes, which are often subtractive, and begin with a cutting away of fabric, or the carving away of the marble that doesn't look like Moses, as Michelangelo is memorably said to have put it.

Trees that let go of their leaves every year are said to be "deciduous." The word appears to be a cousin to "deciding," but my sources tell me otherwise. "Deciduous derives from Latin words meaning "falling away." But the notion of "cutting off" is definitely part of the process here. Trees shed their foliage by what's known as "abscission." This is another fancy Latin-derived term that means essentially "cutting off."

It's a lot of effort for trees to maintain their foliage in extreme weather, and so as winter approaches, they simplify by closing down, as one closes down a summer cottage for the season. Chlorophyll is broken down and its elements reabsorbed into the tree. This disappearance of green lets the yellow, red, and orange colors show through. Nutrients are also reabsorbed from the leaves, and a little "separation layer" forms at the base of each leaf, and detaches it.

When the brilliantly colored leaves fall away, they make room for another kind of beauty, that of the bare trees themselves – graceful, balanced, strong, ever striving upward to the sun, ever rooted deeply in the earth.

It was just a short piece on the radio the other day, about how some people take pains to make themselves invisible on the Internet. They don’t use their real names in chat rooms, the writer for Wired News explained to the NPR host; they don’t join clubs that put their newsletters online. If they do run across themselves on the Internet, they may tweak their names slightly to slip back under the radar of the search engines.

What struck me most about it, though, and seems to have given everyone I’ve discussed it with a chuckle, is the term used in the interview to describe these people cloaked in privacy. They are “ungooglable,” or, as Wired rendered it, “unGoogleable.” (My own preference for a word that is being absorbed into the vernacular would be to lowercase it and drop that middle "e." Google's lawyers are probably not happy with any of this.)

As Ann Harrison wrote in Wired News:

As the internet makes greater inroads into everyday life, more people are finding they're leaving an accidental trail of digital bread crumbs on the web - where Google's merciless crawlers vacuum them up and regurgitate them for anyone who cares to type in a name. Our growing Googleability has already changed the face of dating and hiring, and has become a real concern to spousal-abuse victims and others with life-and-death privacy needs.

And so quickly: The company is less than 10 years old.

By contrast, the humble English word “ship,” as a common noun – very common indeed in the language of a seafaring nation – goes back to the early 8th century. But the oldest citation the Oxford English Dictionary gives for “ship” as a verb in the sense of sending or transporting (goods) by ship dates from 1436: “Saffron, quiksilver … is shipped into Fflaundres fulle craftylye.”

The transition that took seven centuries with “ship” has taken less than a decade with “Google”: “I only ever met him at the coffee shop, so I thought I’d better Google him before our first real date.”

"Google" has been successful as a corporate name because it's been successful as a corporation, of course, but the sound of the word explains part of its appeal, too. It was coined as a variation on "googol," the invented term for a 1 followed by 100 zeros. It was intended as a vast unimaginable number that "everyone" would try to imagine, as the Math Forum at Drexel University explains.

But "Google" works as well as it does for reasons utterly unmathematical. The "oo" sound is heard in words like goofy and doofus and loopy. Barney Google and his friend Snuffy Smith live on, but don't exactly represent the highbrow end of the funny pages.

"Google" fits in easily among a group of words that swing into action as either nouns or verbs: giggle, wiggle, waffle, chuckle, fizzle, tickle – they're not in the dictionary marked "slang", but you don't expect to run across them in, say, a Supreme Court opinion. Whatever "googling" is, it can't possibly be anything that's hard to do.

Corporate names like "American Telephone and Telegraph Company" or "Ford Motor Company" all but cried out to be carved into stone. Compare – and try to explain – eBay, Amazon, and the self-punctuating Yahoo!

Google, like Xerox and FedEx before it, illustrates the paradox of trademark success. The photocopy, in its day, helped flatten the information hierarchy – as anyone who ever received the fifth carbon copy of an important document can attest. FedEx built a business by knowing where things were in transit, but it became a verb of the people when it demonstrated that for few dollars more, that belatedly purchased birthday gift could actually get there on time.

Such trade names don't just define leading companies; they suggest new words to go with the new processes they provide. But when they lend their names to the common speech, the companies sometimes have trouble getting them back.

American history has been the history of people in motion.

As the hurricane-battered Gulf Coast struggles to rebuild, many of those who fled the region are now finding their future in a different place. However dreadful the circumstances of its launch, this wave of migration, like other such waves before it, has the potential for being a great adventure.

At what we might call the retail level, Katrina's diaspora across the country could mean that some Utahns get to see dreadlocks in person for the first time. It will mean the quality of live jazz available rises significantly in many places. And I can't help thinking the great gumbo of accents and influences that is America's spoken language is about to get a mighty stir.

Not that the pot hasn't already been stirred and seasoned with the verbal spice of migrants and immigrants from all over. Sometimes a single characteristic sound or usage pops up in two very different places – the Scottish-influenced "oo" for "ou" ("aboot the hoose") that is heard in Canada is also found in Virginia, for instance.

Similarly, the characteristic New Orleanian accent, sometimes known as "Yat," turns out to have a fair bit in common with "Brooklynese," including the "er" sound that gets pronounced "oi" – as in "Toity-toid Street." Archie Bunker, look out.

The "oi" for "er" substitution isn't part of the Southern accents you hear in the movies. But from the audio archive of memory, I can summon up a couple of voices from my teen years in South Carolina in which that was a distinctive feature. Both cases were of people born probably before 1920, and in one case, very possibly before the turn of the century. I can't recall their having a specific connection to New Orleans, but I do recall one senior lady who spoke of "church work" as "choich woik," and somewhere I'd read that this was a characteristic of New Orleans.

Here's what I found out online about the New Orleans accent:

It is similar to a New York "Brooklynese" accent to people unfamiliar with it. There are many theories to how the accent came to be, but it likely results from New Orleans' geographic isolation by water, and the fact that New Orleans was a major port of entry into the United States throughout the 19th century.

My research enlightened me about "Yat" – people of New Orleans, who greet each other with "Where y'at?" instead of "How are you?" Some see it as a pejorative. But another source called it a"colloquial demonym," and how about that? "Demonym " turns out to be a term for the inhabitants of a place, literally "the name of a people."

And as for "New Orleans" itself – is there a city name that has more semiofficial correct pronunciations? A few weeks ago, when the news was all Katrina all the time, one could sometimes hear four or five different versions of "New Orleans" within a single top-of-the-hour news bulletin: It would start with "Noo OR lins," "Noo Or-LEANS," and Noo OR-lee-ans," and go on from there.

A little Web surfing confirms that I'm not the only one to notice this embarrassment of riches:

In a city whose very name is pronounced in nearly 100 different ways by its citizens, all the way from the filigreed, nearly five-syllable "Nyoo Ahhlyins" to the monosyllabic grunt of "Nawln," it takes a very sensitive ear, not to mention years of practice, to pinpoint the incredible binds the native speaker encounters, those specific words where the slow tongue gives up and makes a leap of faith.

I have a theory that a lot of people encounter the name of the city first in a song as they're growing up, and they tend to pronounce it the way it's pronounced in that song. If you grew up with "The City of New Orleans," that great tune about riding the rails, you have to say "Noo ORlins." If you grew up with "The House of the Rising Sun," you've got to call it "New or LEANS" or it won't scan, or rhyme with "bluejeans" in the third verse.

Americans in motion have been listening to the music of one another's voices for centuries as one accent has rubbed against another. If in the months ahead you hear an expatriate New Orleanian looking for "woik," you'll understand what's meant.