Veil - to cover something, like women have veil to cover their face. Clouds can also veil sun.
Obsidian - dark black.
Murmur - Whisper in quite voice, often to someone in a angry manner Badbadana.
Silhouette - dark outline image against lighter background
Shroud - to cover completely, conceal, it's used when someone die also.
Gloom means dark, desperate and no hope environment.
Flicker is appearing disappearing anything in instant, also something unsteady.
Desolation - deserty, alone, empty.
Eerie - mysterious in scary and supernatural way.
Twilight - dim light between evening and night.
Ominous means something bad is going to happen, something unfortunate.
Arcane means known by few, mysterious for most.
Cryptic also means hard to understand, also refer to code language, that is created intentionally in that way.
Dimly means in low intensity.
Spectral - haunting figure, mostly refering to ghost.
Forlorn:- feeling painful loneliness
Wraith - mostly horror ghostly image
Abyss - something dark bottomless, can be refer to pit or void or emotions.
Linger - something staying long, even after it should be disappeared already.
Hollow - empty inside.