Herculean, abstruse, arduous, backbreaking, brutal, burdensome, complex, critical, crushing, delicate, demanding, difficile, difficult, effortful, exacting, forced, formidable, grueling, hairy, hard-fought, hard, heavy, hefty, intricate, jawbreaking, killing, knotted, knotty, labored, laborious, mean, no picnic, not easy, onerous, operose, oppressive, painful, punishing, rigorous, rough, rugged, set with thorns, severe, spiny, steep, strained, strenuous, thorny, ticklish, toilsome, tough, tricky, troublesome, uphill, wearisome, wicked