difficile

firm, hard, rigid, serious, solid, difficult, stringent, laborious, dogged, adamantine, tough, strict, strong, sticky, troublesome, exquisite, chronic, heavy, formidable, grim, demanding, arduous, ironclad, indomitable, austere, exacting, severe, stout, rugged, grave, intense, violent, callous, inexorable, trenchant, tense, crusty, difficile, trying, dour, intolerable, flinty, stony, petrous, hard-shell, irresistible, insupportable, inflexible, insufferable, labored, steely, rigorous, rocky, unsparing