umbral

Of or like a shadow or shadowy apparition. Derived from the Latin umbra, meaning “shadow”.

Smoke was rising and beginning to coat the clouds a deep, umbral black.

Pertaining to an umbra.

In the classification of the Paleozoic series of Pennsylvania, according to H. D. Rogers, a group of rocks of great thickness, belonging to the Carboniferous, and lying between the Seral or Millstone-grit and the Vespertine.