stygian

A narrow loophole barely filtered through a pale ray of light into that semi-Stygian darkness.

It was not the sort of night we know on earth, but a Stygian blackness.

The night had become inky-black; the town was in a valley and the shadow of trees and houses made the darkness even more Stygian.

One of the Stygian vessels, the Despair, was sunk by the Hope.

Then the Stygian darkness of the great pines grew; and the silence of wonder fell on the two quarrellers.