Occasionally, a sequence of syllables pops into my brain that seems vaguely word-like. I take the syllables and roll them around in my head a bit, hypothesizing a few meanings for this jumble of sounds. I might end up with a quasi-understanding of a maybe-word. This half-knowledge feels like a shadow or a ghost – so insubstantial that I’m not sure if I dreamed this word and its meaning or if, in fact, I actually do know something about an actual, concrete piece of language.

There are also times where a word-like wraith reappears in my consciousness so often that it starts to make my internal word-identifier itch. The only logical response is to actually Google the dang thing to see (a) if it actually is a word and (b) if it is a word, what the heck does it even mean.

Recently, the word crepuscular kept creeping around the edges of my brain, and it was simultaneously so delightful and possibly sinister that I knew that I had to do something with this four-syllable monstrosity. I needed to learn what this word was so that it didn’t trigger temporary insanity the next time its syllables decided to rattle around in my head for a few hours.

Before knowing the actual definition or usage for crepuscular, here are some of my brain’s proposed (and incorrect) definitions:

• an adjective describing a really strong robot
  as in, “The Terminator was quite crepuscular, much like a body builder is muscular”
• an adjective describing something a bit rough and spiky (like a crustacean or tree bark)
• something made up of many tiny units, like a coral reef or a wasp’s nest
  [This is actually much closer to the definition for corpuscle, which is an actual word and not related to ‘crepuscular’ at all. The currently used definition of ‘corpuscle’ describes cellular anatomical units, like individual blood cells; historically, it was used as a description of little tiny bags of light and/or units of matter.]

For whatever reason, I also had a pretty vivid mental image connected to crepuscular: a battered old fishing vessel with peeling paint, splintery seats, and a hull encased in barnacles. This image may have been influenced by all or some of the definitional red herrings described above.

None of this information so far has been useful or accurate, so here is the actual definition.

Crepuscular ([kɹ̥ɛ ‘pʰə skjuː ɫɚ] adjective) is used to describe the space between daylight and darkness. It comes directly from the Latin word for ‘twilight’: crepusculum.

The most common context for crepuscular in modern English is as a descriptor of animal behavior. Animals that are most active during the day are diurnal. Animals most active at night are nocturnal. Animals that are most active at dawn and/or dusk are described as crepuscular.

Crepuscular animal behavior can be further broken down into two categories:

1. Matutinal animals are most active at dawn. Songbirds are perhaps some of the most famous matutinal animals and can be used as a benchmark of this type of behavior. Think Shakespeare’s “lark at break of day arising / From sullen earth” or the proverbial early bird with a wormy breakfast.
2. Vespertine animals include creatures like bats, lightning bugs, and moths, which appear in the evening hours but are not active in the morning.

These words that distinguish between morning twilight and evening twilight are closely related to the names for liturgical prayers at these particular times of day. ‘Matins’ are prayers said or sung in early morning, often before sunrise. ‘Vespers’ (also called ‘evensong’) are prayers said or sung in the evening at or around sunset. Both words come directly from the Latin words meaning morning (matin) and evening (vesper) respectively.

This division of crepuscular behavior into morning and evening categories brings up another new thing that I learned during this word-based adventure of discovery: twilight is not exclusively an end-of-day phenomenon. I assumed that twilight can only happen in the evening because most English speakers use ‘twilight’ to describe the time between sunset and full darkness. However, the literal meaning of twilight is not restricted to an evening interpretation. The twi- part of twilight is recognizably similar to the words ‘twice’ and ‘twin’, and this prefix means something like ‘double’ or ‘both at the same time.’ Literally, twilight means “the time when it is both light and dark at the same time.” Therefore, twilight technically could mean either dusk or dawn.

But language isn’t always logical or technical. For no good (i.e., logical or technical) reason, English speakers prefer to associate the word ‘twilight’ primarily with dusk so that’s the first meaning of twilight that we think of. Even though twilight could also refer to dawn.

You I learn new things every day.

Another fun rabbit trail that I followed when researching the meaning of crepuscular are other words that are used to describe this time between day and night. One such word is this fantastic Middle High German word: zwischerliecht. Not only is this incredibly fun to say in a very bad German accent, but the translations for this word online also caught my eye. The claim is that zwischerliecht has the definition (and I am directly quoting here) “literally tweenlight.”

Now, my initial interpretation of ‘tweenlight’ was that there was some old German word that described that liminal space between daylight and nighttime as a not-quite-teenager sort of light. I got really excited and started wondering if German used the word kinderliecht (‘child-light’) to describe the first rays of sun peeping over the horizon. Also, is the German word for noon some other similar -liecht word that starts with [insert German word for ‘adult’ here]? But then I dug a teeny tiny bit further and realized two important and ultimately disappointing facts:

1. The English use of tween to refer to a child nearing puberty was not a thing until the (late) 20th century, with the most common meaning of ‘tween’ probably being coined in the 1980s. Since Middle High German was spoken in the 11th to 14th centuries, interpreting “literally tweenlight” as a term for light in its prepubescence is wildly anachronistic.
2. A better literal translation of zwischerliecht is “between light.” Why multiple sources decided to use an archaic form of the preposition ‘between’ in their English translation of a Middle High German word, I do not know. Yes, zwischerliecht was a German word used in the period between 1050 and 1350, and, yes, the prepositions ‘tween’, ‘between’, and ‘atween’ were used interchangeably in English during that time period. But no, a reference source defining zwischerliecht in English does not need to use medieval English as part of the definition. That just confuses people.

Alas, ‘tweenlight’ has nothing to do with tweenagers.

End of rabbit trail.

Rabbits are, by the way, a great example of a crepuscular animal, as they tend to be most active at dawn and dusk. Other animals that behave in this way include foxes, housecats, deer, wolves, bobcats, skunks, and opossum. While deer and rabbits can be and sometimes are active at any time of day or night, they tend to wander in search of food most often at crepuscular hours. Some biologists theorize that these prey animals prefer to be most active in low light because they are more easily camouflaged into their environments during these times. A related theory is that predators adapted to be most active at the same time as their prey were active, which is why animals like wolves, foxes, housecats, and other feline predators tend to be crepuscular. Why deer and rabbits did not then adapt to hide out during peak crepuscularity, I have no idea. I am not a biologist.

I now have a better idea of what crepuscular means. To prevent future brain hauntings where I struggle to remember what ‘crepuscular’ means, I have been practicing with this knowledge and created some new mental pictures of ‘crepuscular’ to flesh out this definition.

The first cool breeze of evening touches my skin as twinkling signals of fireflies emerge in the grass.

An exhausted Boy Wonder looks up after a long night of fighting evil. The first rays of dawn signal a brief respite from his labors until darkness falls again over Gotham City.

Wolf-watchers in Yellowstone National Park huddle with binoculars and thermoses of hot coffee in the wee hours of a winter morning, waiting to catch a glimpse of a well-furred pack loping from one part of their territory to the next before the sun fully rises.

You shrug into your jacket and step out the door. The porch light flicks on behind you. You climb into your car with that perfect blend of a contented buzz from interacting with people you love and the anticipation of returning to a space where you can take off your pants. Your friend or maybe your mom calls out a final farewell: “Watch out for deer!”
And that’s its own kind of “I love you” in a lovely, crepuscular sort of way.