Herculean, abrupt, abstruse, backbreaking, brutal, burdensome, complex, critical, crushing, delicate, demanding, difficile, difficult, effortful, energetic, exacting, exhausting, fatiguing, forced, formidable, grueling, hairy, hard, heavy, hefty, intricate, jawbreaking, killing, knotted, knotty, labored, laborious, mean, no picnic, not easy, onerous, operose, oppressive, painful, precipitate, precipitous, punishing, rigorous, rough, rugged, set with thorns, severe, sheer, sideling, spiny, steep, stickle, strained, strenuous, taxing, thorny, ticklish, tiring, toilsome, tough, tricksy, tricky, troublesome, trying, uphill, vigorous, wearisome, wicked