Euphemisms inevitably sprout in the wake of disaster. Consider the word yesterday, which suddenly meant something specific and terrible on April 16, 2013.

I noticed this new yesterday while I was in Boston reporting on the aftermath of the Boston Marathon bombings. People there weren’t calling them “the marathon bombings.” They weren’t calling the attacks anything, really, even though the bombings were all anyone was talking about.

It got me wondering: What determines how we talk about nightmarish events? And what happens once yesterday turns into last month or last year or last century?

But first: Back to April 16, when yesterday was all you had to say. “Yesterday,” or “the thing that happened,” or “it.”

“The purpose of the euphemism is really to alleviate some sense of trouble that you might feel if you were to use more direct language,” the linguist Ben Zimmer told me; it’s a way of “covering up or avoiding deeper emotions.”

Essentially, swapping direct language for more innocuous terms helps diminish the reality of horrific events as we process them. (Incidentally, euphemism comes from the Greek for “good omen.”) When a subject matter is taboo — because it’s either socially unacceptable or emotionally fraught — we invariably find ways of talking clearly about the subject without being explicit.

We do this all the time: “A long illness” continues to be used in the place of cancer as the cause of death in obituaries. (Just this week, actor Angelina Jolie wrote this about her preventative double mastectomy: “Cancer is still a word that strikes fear into people’s hearts, producing a deep sense of powerlessness.”) The decades-long period of violence spurred by sectarian conflict in Northern Ireland in the late twentieth century is collectively known as “The Troubles.” In Uganda, someone who has HIV or AIDS is said to be “slim.” “Under the weather” is an old-school shorthand for drunk or otherwise indisposed.

Reliance on euphemism comes up in fiction, too. In the Harry Potter series, frightened wizards called the villain “You-Know-Who” and “He-Who-Must-Not-Be-Named” and avoided saying Voldemort.

“For a long time, people actually thought words had magical powers,” University of Michigan linguistics and philosophy professor Ezra Keshet told me. “And even people who don’t think that still get a strange feeling from upsetting or powerful words.”

One of the best-known euphemisms in recent history is 9/11.

“It’s just numbers, right?” Zimmer says. “It’s something that allows us to treat it without thinking about what happened that day by just using the numbers.”

The term also works because it simplifies a complex series of attacks across a wide region. Whereas the types of shorthand for other violent acts — say, Columbine or Virginia Tech — are place-name based, the September 11 attacks struck New York, Pennsylvania, and Virginia. (Though Wikipedia will redirect a search for “9/11" to its “September 11 attacks” page.)

“So the only thread that tied [the attacks that struck several locales] together was the date,” Keshet said. Then he gave me an idea: Why not try to find the earliest reference to 9/11, to better understand how it took hold?

It turns out “9/11" emerged almost immediately after the attacks. The New York Times ran a column by Bill Keller on September 12, 2001, that had the headline “America’s Emergency Line: 9/11,” a reference to the date of the attack and an allusion to 9-1-1, the phone number Americans dial to reach emergency responders.

“The dual meaning of 9/11 was so obvious and inevitable that I’d never presume to take credit for it,” Keller told me.

Actually, he says the idea came from a conversation he overheard in New York City on that fateful day. Keller’s role as an op-ed columnist at the Times was brand-new, and he hadn’t planned to file his inaugural column — “a wonky piece on a water dispute in Oregon. Don’t ask.” — for another couple of weeks. But after he picked up his son from school in the wake of the attacks, he got a call from his editor, Gail Collins.

“She said they were asking all the columnists to write for the next day,” Keller said in an e-mail. “So my brain was already cogitating when, a little later, I overheard someone on the street remark on the 9/11 (911) coincidence… Though columnists generally have the prerogative of writing their own headlines, I think I simply slugged it ‘9/11' and a copy editor enlarged it into ‘America’s Emergency Line: 9/11' to fit the page configuration.”

Another way that 9/11 resonates: The imagery of the 11 is a visual parallel to the twin towers of the World Trade Center that collapsed that day in New York City. The term also became a cultural and political marker, the splitting point from which a pre-9/11 reality gave way to the post-9/11 world.

“So it has this larger cultural meaning as well,” Zimmer said. “9/11 became its own kind of brand.”

The branding of disasters — that is, determining and amplifying a common message — is a major part of how we talk about them. Bostonians are now being inundated with “Boston Strong” merchandise, for example. Whether such items are an invitation to talk about what’s happened or a way to wordlessly acknowledge tragedy depends on the individual wearing it.

Zimmer has been thinking about the language behind these branding efforts a lot lately. Over the weekend he wrote about “Boston strong,” the unifying phrase that has become a slogan of sorts — splashed across baseball caps, Onesies, even scented candles — since the marathon bombings. (If the merchandising of tragedy makes you uneasy, you’re not alone.)

“It has this kind of commercial appeal,” Zimmer explains. “It’s showing up on T-shirts and ribbons and hats. And it has this feeling of coming out of nowhere.”

But Zimmer points out that “_____ Strong” has been around for a while. The U.S. military started using the recruiting slogan “Army Strong” back in 2006. Lance Armstrong’s “Livestrong” campaign began in 2004. More recently we’ve seen “Vermont Strong” after Hurricane Irene and “New Jersey Strong” following Sandy.

“Another rhetorical frame is ‘we are all blank now,’” Zimmer says. “Like, ‘We are all Bostonians.’ That one has quite a long history to it. Certainly since 9/11 you were getting, ‘We are all New Yorkers.’ When the Virginia Tech shootings happened, you had, ‘We are all Hokies.’ This show of solidarity becomes a very common trope, this fill-in-the-blank category that makes us feel like we somehow have this common bond with those who were affected.”

Rhetorical showings of solidarity are often paired with a sense of urgency about remembering what has happened. (“Never forget” has become so ubiquitous that it has at times become a parody.)

“‘Remember the blank’ has a long history,” Zimmer says. “‘Remember the Alamo,’ ‘Remember the Maine’: You’re not letting the memory of some event go.”

Using calendrical shorthand to refer to a disaster seems inherently part of this push to remember, because knowing an event by its date is in itself a means of ensuring commemoration. Similarly to 9/11, the 2005 London bombings are widely known as 7/7 because they occurred on July 7. (Zimmer points out that the repeating sevens alleviate the potential for confusion, as Europeans typically put the day of month before the month itself in writing a date, the opposite of the American format. In European countries, 9/11 would have been 11/9, for example. To further confuse matters, some have referred to the toppling of the Berlin Wall — on November 9, 1989 — as 11/9.)

So why do we call the 1941 attack on the U.S. naval base on Oahu, Hawaii, “Pearl Harbor” instead of “12/7,” particularly when President Franklin Roosevelt declared it the “date which will live in infamy”? Did Londoners coin the term 7/7 because the bombings on that date happened so soon after 9/11? And why is the March 11, 2011, Japanese tsunami only sporadically remembered as 3/11?

Keshet poses a broader question: “How does a speech community as a whole ‘decide’ to name an event?”

He identifies three steps in the process:

  1. Referring to something salient about the event, like the date or location.
  2. Bleaching any social taboo from the name.
  3. Having some influential speakers, such public officials and members of the news media, repeat the term.

But it’s not always up to the “speech community” to decide. There are plenty of prepackaged disasters. Hurricanes get their names from the World Meteorological Organization, for example.

“It’s interesting to see how that process ends up charging those names with new connotations,” Zimmer says. “You can’t talk about [the name] Katrina without thinking of [Hurricane] Katrina. With Sandy, it seemed like Sandy was not an appropriate name for such a devastating storm.”

Nor appropriate, many agreed, was the term Frankenstorm, a nickname that caught on when Hurricane Sandy was still swirling over the Atlantic Ocean. News organizations like CNN banned the cutesy nickname, believing it trivialized the gravity of a dangerous storm.

Ultimately, Hurricane Sandy — which technically stopped being a hurricane once it made landfall — became Superstorm Sandy. But in New York and New Jersey, people still just say Sandy with a level of familiarity that might not make as much sense in a place that didn’t experience it firsthand. (Similarly, Iniki might not mean anything to you, but people still use the 1992 hurricane’s name as shorthand in conversations about the most powerful ever to hit Hawaii.)

So, geography matters. People talk about disasters in different ways depending on their proximity to the event.

“It’s like the old joke,” Zimmer says: “‘In China, they don’t call it Chinese food. Its just food.’ So there’s something interesting about the labels that outsiders give versus those that people who directly experience it do.”

Eight years after Hurricane Katrina devastated New Orleans, few people in that city will say the name of the hurricane. When I was there last month, a friend explained: “No one says Katrina here. It’s almost superstition. It’s always just ‘The Storm.’”

That may offer some comfort to the Katrinas out there whose name is now synonymous with the tragedy.

I remember standing by the bar at a pizza joint in Newtown, Connecticut, last December — days after the horrific elementary school shooting there — when I heard a local man lamenting the new meaning his town’s name would take on.

“You know Columbine?” the man said to his buddies. “That’s Newtown now. When you say you’re from Newtown, that’s what it will be like.”

There’s no question that people associate Newtown with the massacre in the town. But there are frequent references to Sandy Hook, the name of the school where the rampage specifically took place.

“You get the sense that people in the news media or other observers are trying to figure out in the wake of a tragedy what to call it,” Zimmer says. “Though 9/11 happened very quickly, with Newtown, was it Newtown or was it Sandy Hook? It’s still kind of both.”

Naming conventions also change over time. Consider World War I, which only got that name once World War II had happened. Before that it was “The Great War” or “The War to End All Wars.”

“To call it that, you’re making a political statement that this isn’t going to happen again, which of course it did,” Zimmer says. “This question of labeling is something that people in the media feel very strongly about too: ‘What do we call this thing?’”

Creating a narrative compels reporters and editors to develop names for the things they’re writing about.

The writer Michelle McNamara explored this concept in a Los Angeles Magazine piece about tracking a lesser-known California serial killer, whom she calls the Golden State Killer. (Wikipedia still classifies the killer primarily as the Original Night Stalker.)

Does it follow, then, that media-rich environments also are more likely to have pithy names emerge for their disasters? Maybe. Consider a country like Mali, where there isn’t a crushing media presence.

“Most of the bad things that happen to [Malians] are droughts or locusts, or something that has to do with starvation,” says Jeffrey Heath, a historical-linguistics professor at the University of Michigan who focuses on the West African country. “The name of it gets passed down and it’s just a thing like ‘the year we ate roots,’ or some description like that.”

A swarm of locusts may not earn a nickname short enough for a headline in Mali, but it does in New York City. As the East Coast braces itself for a seventeen-year brood of cicadas to emerge from underground, the media has already branded the event “Swarmageddon.”

Or is it “Cicadapocalypse”?

The irony, Zimmer says, is that the actual name used by scientists may be the best one of all.

“My brother is a science writer,” Zimmer says. “He says that the official name of it is Brood II. It sounds like some sequel to an awesome science-fiction novel. Perfect.”