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Long ago, when people believed that everything was made up of four elements—earth, air, fire, and water—they thought the stars and planets were made up of yet another element. In the Middle Ages, people called this element by its Medieval Latin name, quinta essentia, literally, "fifth essence." They believed the quinta essentia was essential to all kinds of matter, and if they could somehow isolate it, it would cure all disease. People have since given up on that idea, but English users have kept quintessence, the offspring of quinta essentia, as a word for the purest essence of a thing. Some modern physicists have given quintessence a new twist—they use it to refer to a form of the dark energy believed to make up almost 70 percent of the energy in the observable universe.

Franz Kafka (1883-1924) was a Czech-born German-language writer whose surreal fiction vividly expressed the anxiety, alienation, and powerlessness of the individual in the 20th century. The opening sentence of his 1915 story The Metamorphosis has become one of the most famous in Western literature (“As Gregor Samsa awoke one morning from uneasy dreams he found himself transformed in his bed into a gigantic insect”), while in his novel The Trial, published a year after his death, a young man finds himself caught up in the mindless bureaucracy of the law after being charged with a crime that is never named. So deft was Kafka’s prose at detailing nightmarish settings in which characters are crushed by nonsensical, blind authority, that writers began using his name as an adjective a mere 16 years after his death. Although many other literary eponyms, from Austenian to Homeric, exist and are common enough, Kafkaesque gets employed more than most and in a wide variety of contexts, leading to occasional charges that the word has been watered down and given a lack of specificity due to overuse.

If you guessed that quixotic has something to do with Don Quixote, you're absolutely right. The hero of Miguel de Cervantes' 17th-century Spanish novel El ingenioso hidalgo don Quijote de la Mancha (in English "The Ingenious Hidalgo Don Quixote of La Mancha") didn't change the world by tilting at windmills, but he did leave a linguistic legacy in English. The adjective quixotic is based on his name and has been used to describe unrealistic idealists since at least the early 18th century. The novel has given English other words as well. Dulcinea, the name of Quixote's beloved, has come to mean "mistress" or "sweetheart," and rosinante, which is sometimes used to refer to an old horse, comes from the name of the hero's less-than-gallant steed, Rocinante.

Being but humble lexicographers, we cannot say whether an apple a day truly keeps the doctor away, but as far as regimens go, one could do a lot worse than snackin’ on a McIntosh. Regimen, which usually refers to a system of rules or guidelines—often for living a healthy life or taking a regular dose of exercise—comes ultimately from a Latin verb, regere, meaning “to direct.” Regere_led in apple-pie order to the English word regimen, first by way of the Latin noun regimen, meaning “steering” or “control,” and then via the Medieval Latin regimen, referring to a set of rules. Other regere descendants fell further from the tree, including correct, erect, region, rule, and surge. Be sure not to confuse regimen with another of its kin, regiment, which refers to a military unit, as doing so could upset the apple cart.

Across time and across cultures—as evidenced from Chauvet-Pont d’Arc’s paintings to The Lion King — lions have captured people's imaginations. Though the big cats themselves are fascinatingly complex, it’s perhaps no surprise that humans have long projected qualities of bravery and regality upon the proverbial "king of the beasts". It is precisely those and similar admirable qualities that led, in the 18th century, to lion being used for a person who is similarly well-regarded, especially after a long and distinguished career in a particular field, as in "lion of the Senate", or "literary lion". This sense of lion the verb lionize, which first appeared in English in the early 19th century to apply to acts of treating someone as, perhaps, deserving of roaring applause.

Grok may be the only English word that derives from Martian. Yes, we do mean the language of the planet Mars. No, we're not getting spacey; we've just ventured into the realm of science fiction. Grok was introduced in Robert A. Heinlein's 1961 science fiction novel Stranger in a Strange Land. The book's main character, Valentine Michael Smith, is a Martian-raised human who comes to Earth as an adult, bringing with him words from his native tongue and a unique perspective on the strange ways of earthlings. Grok was quickly adopted by the youth culture of America and has since peppered the vernacular of those who grok it.

When you reach the zenith, you're at the top, the pinnacle, the summit, the peak. Zenith developed from an Arabic phrase meaning "the way over one's head" and then traveled through Old Spanish, Medieval Latin, and Middle French before arriving in English. As long ago as the 1300s, English speakers used zenith to name the highest point in the celestial heavens, directly overhead. By the 1600s, zenith was being used for other high points as well. The celestial term is often contrasted with nadir, which refers to the point that is vertically downward from the observer (imagine a line going through the Earth from the observer's feet and out the other side into the sky). Figuratively, nadir simple means "the lowest point".