Boomers, Generation X, millennials—every 20 years or so we name a new generation. We characterize them by cultural shifts in fashion (bell-bottoms!), musical styles (grunge!), and food preferences (kale!). But generations can also be characterized by language, as seen in a new book by Allan Metcalf, From Skedaddle to Selfie, out in November from Oxford University Press. The expressions that rise to prominence at particular times often reveal surprising things about who we are.

When the nation was young, members of the Transcendental Generation (born 1792 to 1821) had a spiritual, authority-questioning bent. They brought transcendental into the general vocabulary. They also, writes Metcalf, “bequeathed to the country its greatest and most successful word”: OK. First used by a Boston newspaper editor as an intentionally misspelled, jokey abbreviation of “all correct”—similar to the publishing industry’s term TK to indicate material “to come”—the expression took off during the 1840 re-election campaign of Martin Van Buren, who was also known as Old Kinderhook. His supporters set up OK clubs, jauntily suggesting he was “oll korrect.” Detractors quickly turned the new word around to criticize Van Buren (he’s “orfully konfused!”) and his predecessor Andrew Jackson (so illiterate he couldn’t spell all correct!). Eventually everyone forgot where OK came from, and it became an all-purpose staple.

After the Transcendentals came the Gilded Generation (born 1822 to 1842). They were “gilded” since they would witness great economic expansion. During the Civil War, they coined skedaddle as a mocking description of an enemy beating a “hasty and disorganized retreat.” When the Union army was defeated at the Battle of Bull Run, Southerners referred to the retreat as “The Great Skedaddle.” Northerners threw the insult right back: A newspaper report called it “a phrase the Union boys up here apply to the good use the seceshers make of their legs in time of danger.” This made-up word with a silly sound brought a little levity in dark times.

Born around the upheavals of war, the Missionary Generation (born 1860 to 1882) became idealistic, politically active adults. They gave us sweatshop in their fight for workers’ rights. Not all new words were so serious: The Missionaries also gave us fan. In 1885, a sportswriter was compelled to explain that fan was “base ball slang” for fanatic. That explanation soon became unnecessary.

The Lost Generation (born 1883 to 1900) had to contend with World War I as they came of age. They seemed to have lost their way spiritually and, according to their elders, morally. They filled the Roaring ’20s with words like flapper, speak-easy, and jazz—and they were also the first to use sexy. According to Metcalf, “until the 20th century, nobody was sexy.” At first the word described risqué content or temptations—like “sexy” magazines, books, or plays—or the feelings they might inspire. Later it became an approving way to describe a person, and anything generally exciting.

The GI Generation (born 1901 to 1924) fought World War II or stayed home and rationed, scrimped, and saved to help the war effort. People started to smuggle home their restaurant leftovers to give to the family pet. “And so to prevent loss of napkins, or perhaps to encourage patriotic frugality,” restaurants started providing doggie bags.

Trick or treat came from the Silent Generation, born during the Great Depression. Characterized as sedate and ready to conform, they became bobby-soxers and wore gray flannel suits, but as kids they coined the common Halloween request, which was a bit more polite than the previous “Shell out!”

Tooth fairy took flight with the Boomer Generation (born 1943 to 1960), who also gave us hippie, yuppie, psychedelic, and groovy. They lost their baby teeth in a time of optimism, prosperity, Disney films, and Tinkerbell. A fairy-run cash-for-teeth scheme made perfect sense (the going rate then was 10 cents a tooth). A generation can also reinvent an old word. Fun was a noun long before the slackers and hackers of Generation X (born 1961 to 1981) existed, but their generation turned it into a full adjective, injecting it into “a fun time,” “a fun call,” “a fun concert,” and the wealth of other types of fun to be had.

Most recently, the so-called Homeland Generation (born 2005 and later) has been doing something different with wait, using it for statements and questions alike. Metcalf noticed his grandson saying things like, “Wait ... where are we going?” and “Wait ... I’m going over to the neighbor’s house.” It’s both a pause and a request for attention, and it’s “reminiscent of [Metcalf ’s own] Silent Generation’s thoughtful approach to the world.” Is the newest generation articulating a distinctive way of viewing the world? It’s too early to tell, Metcalf concludes: “We’ll have to wait.”