Herculean, abstruse, adverse, antagonistic, arduous, brutal, complex, conflicting, contrary, counter, counteractive, critical, delicate, demanding, detrimental, difficile, difficult, exacting, formidable, hairy, hard-earned, hard-fought, hard, harmful, hostile, in opposition, inimical, intricate, jawbreaking, knotted, knotty, laborious, mean, miserable, no picnic, operose, opposed, opposing, opposite, rigorous, rough, rugged, set with thorns, severe, sinister, spiny, steep, strenuous, stressful, thorny, ticklish, toilsome, tough, tricky, troublesome, troublous, trying, unfavorable, untoward, uphill, wicked, wretched