Uncannily or threateningly dark or obscure.

Roget 421: dark, darksome^†, darkling; obscure, tenebrious^†, sombrous^†, pitch dark, pitchy, pitch black; caliginous^†; black etc. (in color) 431.    sunless, lightless etc. (sun) (light), etc. 423; somber, dusky; unilluminated etc. (illuminate) etc. 420^†; nocturnal; dingy, lurid, gloomy; murky, murksome^†; shady, umbrageous; overcast etc. (dim) 422; cloudy etc. (opaque) 426; darkened; etc. v.. dark as pitch, dark as a pit, dark as Erebus [Lat.].    benighted; noctivagant^†, noctivagous^†.    ... show more

poetic Occurring in the dark or night.