hellacious

1 extreme in degree, power, or effect the hellacious heat was more than we could bear Synonyms acute, almighty, blistering, deep, dreadful, excruciating, explosive, exquisite, fearful, fearsome, ferocious, fierce, frightful, furious, ghastly, hard, heavy, heavy-duty, intense, intensive, keen, profound, terrible, vehement, vicious, violentRelated Words accentuated, aggravated, concentrated, deepened; emphasized, enhanced, heightened, intensified, magnified; stressed; exhaustive, thorough; harsh, rigorous, severeNear Antonyms feeble, weak; shallow, superficial; moderated, qualified; alleviated, eased, lightened, toned (down); abated, decreased, diminished, lessened, reduced, subduedAntonyms light, moderate, soft

2 requiring considerable physical or mental effort the pioneers survived a particularly hellacious river crossing with their covered wagon barely in one piece Synonyms arduous, Augean, backbreaking, challenging, demanding, difficult, effortful, exacting, formidable, grueling (or gruelling), heavy, hard, herculean, killer, laborious, moiling, murderous, pick-and-shovel, rigorous, rough, rugged, severe, stiff, strenuous, sweaty, tall, testing, toilsome, tough, uphillRelated Words abstract, abstruse, complex, complicated, elusive, hairy, insoluble, intricate, involved, knotty, opaque, problematic (also problematical), recondite, serious, spiny, stubborn, thorny, ticklish, tricky; bruising, burdensome, exhausting, labored, onerous, oppressive, stressful, taxing, tight, trying; annoying, bothersome, distressing, irksome, troublesome, vexatious; grievous, grim, strict, stringent; brutal, cruel, inhuman, painfulNear Antonyms achievable, clear, doable, elementary, manageable, uncomplicated; comforting, gentle, painless, relaxed, smooth, soothing; accessible, friendly, idiotproof, user-friendlyAntonyms cheap, easy, effortless, facile, light, mindless, simple, soft, undemanding