Tenebrous
Etymology
From Latin "tenebrosus" ("dark, gloomy"), from "tenebrae" ("darkness, shadows"). It reached English through Old French and has always carried the sense of thick, shadowy gloom rather than mere absence of light.
adjective · /TEN-uh-brus/
Dark, shadowy, and gloomy.
What it names
The word for a heavy, murky darkness — deep woods at night, an unlit vault, a brooding atmosphere.
Example
They descended into the tenebrous depths of the cellar with a single lantern.
Related idea
Murky stresses darkness that is also cloudy or hard to see through; tenebrous stresses deep, gloomy shadow.