lowering

bedimmed, befogged, blackened, darkened, darksome, dim, dimmed, dulled, dusky, misty, murky, obscure, obscured, overshadowed

sunless

black, bleak, cheerless, dark, desolate, dismal, drear, dreary, funereal, gloomy, glum, gray (also grey), sepulchral, somber (or sombre), sullen

bleak, cold, hostile, inhospitable, inimical, unfriendly, unsympathetic

adamant, bound, determined, firm, intent, purposeful, resolute, resolved, steadfast, unflinching

fixed, hard, hardened, hardheaded, immovable, implacable, inflexible, ironhanded, mulish, obdurate, obstinate, rigid, self-willed, set, stiff, stubborn, unbending, uncompromising, unrelenting, unyielding, willful (or wilful)

immutable, unchangeable

black, cheerless, dark, gloomy, glum, joyless, melancholic, moody, morose, sulky, sullen, surly

brooding, grave, humorless, melancholy, serious, sober, sobersided, solemn, somber (or sombre), staid, unsmiling, weighty