Merriam-Webster's Word of the Day for September 23, 2023 is:

tenebrous • \TEN-uh-brus\  • adjective

Tenebrous is a formal word that is often used as a synonym of gloomy. It also can be used to describe dark, unlit places (as in “the tenebrous abyss”) or things that are difficult to understand (as in “a tenebrous tangle of lies”).

// The neighborhood children made sure never to approach the abandoned mansion, which sat tenebrous and foreboding at the top of the hill.

// A horror film seems incomplete without someone running through a tenebrous forest or alley.

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Examples:

“On the heels of Greig Fraser’s spectacular work on Dune, the cinematographer gives the film a moody, tenebrous look to match the tortured pit of Batman’s soul, and production designer James Chinlund’s world-building is first-rate, weaving together elements from real cities and sets to form a Gotham that resembles New York while establishing its own gritty, gothic identity, pulsing with menace and mystery.” — David Rooney, The Hollywood Reporter, 28 Feb. 2022

Did you know?

Tenebrous can mean both “obscure” and “murky,” but its history is crystal clear. Etymologists know that the word comes from the Latin noun tenebrae, meaning “darkness.” Tenebrous has been used in English since the 15th century, and in subsequent centuries has been joined by some interesting and even less common relations. Tenebrionid is the name that may be given to any of at least 20,000 species of mostly nocturnal beetles, also called darkling beetles, many of whom love inhabiting dark places. Tenebrism refers to a style of painting—associated especially with the Italian painter Caravaggio—in which most of the figures are engulfed in shadow while some are dramatically illuminated by concentrated light. And let’s not forget the terrific tenebrific, a tenebrous synonym.