tragic, disastrous, calamitous, catastrophic, cataclysmic, ruinous, devastating, dire, ghastly, awful, unfortunate, dreadful, horrible, terrible, horrific, hideous, horrendous, frightful, atrocious, abominable, abhorrent, gruesome, grisly, monstrous, nightmarish, heinous, harrowing, wretched, woeful, direful
3. (of a period of time or situation) characterized by tragedy, unhappiness, or unpleasantness.
"the dark days of the war"
"a dark vision of the future"
gloomy, dismal, pessimistic, negative, defeatist, downbeat, gloom-ridden, cynical, bleak, grim, fatalistic, black, somber, drab, dreary, despairing, despondent, depressed, dejected, demoralized, hopeless, cheerless, joyless, melancholy, glum, lugubrious, Eeyorish, grave, funereal, morose, mournful, doleful, suspicious, distrustful, doubting, alarmist(of an expression) angry; threatening.
"Matthew flashed a dark look at her"
moody, brooding, sullen, dour, glum, morose, sulky, frowning, scowling, glowering, angry, forbidding, threatening, ominous
suggestive of or arising from evil characteristics or forces; sinister.
"so many dark deeds had been committed"
evil, wicked, sinful, immoral, wrong, morally wrong, wrongful, bad, iniquitous, ungodly, unholy, irreligious, unrighteous, sacrilegious, profane, blasphemous, impious, godless, base, mean, vile, shameful, discreditable, unspeakable, foul, monstrous, shocking, outrageous, atrocious, abominable, reprehensible, hateful, detestable, despicable, odious, contemptible, horrible, heinous, execrable, diabolical, diabolic, fiendish, vicious, murderous, barbarous, black, rotten, perverted, reprobate, sordid, degenerate, depraved, dissolute, dishonorable, dishonest, unscrupulous, unprincipled, crooked, bent, warped, lowdown, stinking, dirty, shady, malfeasant, dastardly, peccable, egregious, flagitious
4. hidden from knowledge; mysterious.
"a dark secret"
mysterious, secret, hidden, concealed, veiled, unrevealed