strenuous

1 marked by or uttered with forcefulness parents who voiced strenuous objections to the new textbooks Synonyms aggressive, assertive, dynamic, energetic, forceful, full-blooded, muscular, resounding, emphatic, vehement, vigorous, violentRelated Words decided, insistent, marked, pointed; absolute, categorical (also categoric), clear, plain, unambiguous, unequivocal; arresting, compelling, conspicuous, impelling, noticeable, strikingNear Antonyms guarded, mild, uncompelling, weak, wishy-washy; ambiguous, equivocal, halting, hesitant; understatedAntonyms nonassertive, nonemphatic, unemphatic

2 requiring considerable physical or mental effort a strenuous workout on the obstacle course Synonyms arduous, 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, hard, 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