laborious

active, assiduous, bustling, diligent, employed, engaged, hopping, industrious, laborious, occupied, sedulous, tied-up, working

knee-deep, swamped; animated, astir, buzzing, flourishing, happening, humming, lively, thriving, vibrant; absorbed, concentrating, engrossed, focused ( focussed), immersed, intent, preoccupied; alive, functional, functioning, going, living, operating, operational, operative, running; energetic, vigorous; hardworking; indefatigable, tireless, untiring

free; asleep, dormant, latent, lifeless, quiescent, sleepy; inert, passive; dead, dull, slow; inoperative, nonoperating

arduous, Augean, backbreaking, challenging, demanding, difficult, effortful, exacting, formidable, grueling ( gruelling), heavy, hellacious, herculean, killer, laborious, moiling, murderous, pick-and-shovel, rigorous, rough, rugged, severe, stiff, strenuous, sweaty, tall, testing, toilsome, tough, uphill

abstract, abstruse, complex, complicated, elusive, hairy, insoluble, intricate, involved, knotty, opaque, problematic ( 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, painful

achievable, clear, doable, elementary, manageable, uncomplicated; comforting, gentle, painless, relaxed, smooth, soothing; accessible, friendly, idiotproof, user-friendly

arduous, burdensome, challenging, exacting, grueling ( gruelling), killing, laborious, onerous, persnickety, taxing, toilsome

difficult, formidable, hard, herculean, rough, rugged, stiff, strenuous, testing, tough; oppressive, trying; rigid, rigorous, severe, stern, strict, stringent

easy, effortless, facile, simple, smooth