challenging

1 requiring considerable physical or mental effort an exceptionally challenging brainteaser Synonyms arduous, Augean, backbreaking, hard, 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 a challenging test designed to whittle down the number of contestants Synonyms arduous, burdensome, demanding, 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