cataclysmal

1 bringing about ruin or misfortune a cataclysmal decision to plunge the nation into war Synonyms calamitous, fatal (or cataclysmic), catastrophic, damning, destructive, disastrous, fateful, ruinous, unfortunateRelated Words apocalyptic (also apocalyptical); hapless, ill-fated, ill-starred, luckless; adverse, baleful, baneful, damaging, deleterious, detrimental, evil, harmful, hurtful, ill, injurious, noxious, pernicious, prejudicialNear Antonyms fluky (also flukey), fortuitous, fortunate, happy, lucky, providential; auspicious, bright, encouraging, fair, golden, heartening, hopeful, optimistic, promising, propitious, rose-colored, rosy, upbeat

2 causing or tending to cause destruction a cataclysmal landslide that virtually wiped out the village Synonyms annihilatory, calamitous, destructive (or cataclysmic), devastating, devastative, disastrous, ruinousRelated Words antibiotic, biocidal; baleful, deadly, deathly, fatal, fell, killer, lethal, mortal, murderous, pestilent, poisonous, virulent, vital; deleterious, detrimental, harmful, perniciousNear Antonyms preservative, protective; constructive, creative, formative, productive; harmless, innocent, innocuous, inoffensive; ameliorative, helpful, useful; healthful, healthy, nonfatal, nonlethal, salubrious, wholesomeAntonyms nondestructive

3 marked by sudden or violent disturbance the French Revolution was one of the great cataclysmal events in modern history Synonyms convulsive (or cataclysmic), stormy, tempestuous, tumultuous, turbulentRelated Words fitful, spasmodic, sporadic; boisterous, clamorous, furious, noisy, riotousNear Antonyms calm, peaceful, placid, serene, tranquil, undisturbed, unperturbed, unshaken, untroubled