arduous

1 requiring considerable physical or mental effort climbing Mount Everest is an arduous, exhausting challenge Synonyms hard, Augean, backbreaking, challenging, demanding, difficult, effortful, exacting, formidable, grueling (or gruelling), heavy, hellacious, 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

2 requiring much time, effort, or careful attention the arduous task of doing the research for my term paper Synonyms demanding, burdensome, challenging, exacting, grueling (or gruelling), killing, laborious, onerous, persnickety, taxing, toilsomeRelated Words difficult, formidable, hard, herculean, rough, rugged, stiff, strenuous, testing, tough; oppressive, trying; rigid, rigorous, severe, stern, strict, stringentNear Antonyms easy, effortless, facile, simple, smoothAntonyms light, nondemanding, unchallenging, undemanding