adamant, adamantine, apply, arduous,
beamy, bitterly, burdensome, callous, difficult, fatigue, firm, formidable, grave, grievous, hard, hard-boiled, hard-core, hardboiled, hardcore, hardship, harsh, heaviest, heavily, heavy, heavyweight, hulking, intricate, knotty, landed, logy, outrageous, pain, ponderous, rigid, serious, severe, stiff, stodgy, strenuously, strong, sweat, thick, toil, tough, trouble, weighty