Synonyms and related words :
Herculean, abstruse, arduous, brutal, complex, critical, delicate, demanding, difficile, difficult, exacting, formidable, hairy, hard, hard-earned, hard-fought, intricate, knotted, knotty, laborious, mean, no picnic, not easy, operose, polysyllabic, rigorous, rough, rugged, sesquipedal, sesquipedalian, set with thorns, severe, spiny, steep, strenuous, thorny, ticklish, toilsome, tough, tricky, uphill, wicked