One of my daughter’s favorite words is petrichor, which is the smell of rain after a dry spell. Rain on a dusty road. Rain on withered grass. Rain interacting with the oils on plants and in the ground and, sometimes, mixing with ozone during a lightning storm. You don’t smell rain when it falls from the sky. And you don’t smell it when it’s been raining a while, say in November. But in late summer, after a long dry spell? That’s petrichor—a word that was invented in 1964 by two Aussie scientists who coined the phrase as a combination of the Greek words for rock (petra) and the blood of gods (ichor).

My wife is partial to crepuscular. Your cat is crepuscular. Any creature that becomes active around twilight is crepuscular. In high school, my friends and I were often crepuscular, especially in the summertime once we got our driver’s licenses. To me, the most intriguing time of day at the local fair is dusk, when the lights on the carnival rides begin to take possession of the midway, the air gets thinner and shadows blend into ephemera. Cats on the prowl and riders on the Tilt-a-Whirl are crepuscular emanations in the waning day.

The odd thing about crepuscular is that it seems as if it should be onomatopoeic (another great word), but it’s not. I expect it to describe something tortoise-like, with a hard shell or carapace. I expect it to have an etymology that combines muscular with creep. But really it’s just a Latin derivative for “twilight” (crepusculum). So rather than being onomatopoeic, it’s mostly taxonomic. Whatever the case, my cat doesn’t care.

Recently, I came upon the word serotinal, which means late summer. It can be used for certain kinds of plants that bloom at this time of year. It can also suggest a feeling of melancholy as the summer winds down. A serotinal nostalgia, for instance. And it sounds like a new pharmaceutical you might ask your doctor about. Feeling overly wistful? Experiencing extreme cases of longing? Try Serotinal! (Side effects may include nausea related to the consumption of fair snow cones, a soul-crunching lack of drive to clean the gutters before October, and excessive remembering of one’s halcyon days. If remembering persists longer than four hours, call your doctor.)

No other season ends with such pensiveness. Fall turns to winter right around the time the holidays kick in and the first snows arrive. Winter ends with spring, and the last snow of the year is rarely mourned. Spring turns to summer, and school is out, vacations commence, and shorts and flip-flops rule the day. And summer does what at the end? It falls, and we are booted out of Eden.

There is usually a point, however, at which summer begs us to leave it behind. If the heat has been excessive, the air muggy or filled with the smoke of regional wildfires, it’s time for a change.

And, now, the air is clearing. School has started. Autumn scratches at the door like a hungry cat.

To be sure, green still clings to the trees, as the sun vectors toward another equinox. Summer has but a few days left, and there’s a serotinal feeling in the air, bearing with it a certain trepidation about what the fall might (or might not) bring.