“Caliginous” is an adjective used to evoke misty, dark obscurity in a poetic manner. Its Latin root, “cālīginōsus,” is based on the noun “cālīgō,” which refers to fog, mist, and vapor. The English adjective describes the state of not being able to see clearly, but not because of darkness. Instead, it’s because the air is full of something like fog or smoke that impedes a clear view. When “caliginous” is used poetically to describe darkness, it describes a darkness that is so thick and enveloping, it is almost physical.