Tough

brawny cohesive conditioned dense durable fibrous firm fit flinty hard hard as nails hard-bitten hardened hardy healthy indigestible inflexible leathery lusty mighty molded resilient resistant rigid robust rugged seasoned sinewy solid stalwart steeled stiff stout strapping tenacious tight tough as nails unbreakable unyielding vigorous withstanding

adamant arbitrary callous confirmed cruel desperate drastic exacting ferocious fierce firm fixed hard hard-bitten hard-boiled hard-line hard-nosed hard-shelled harsh headstrong immutable inflexible intractable merciless narrow obdurate pugnacious refractory resolute ruffianly ruthless savage severe stern stiff strict stubborn taut terrible unalterable unbending uncompromising uncontrollable unforgiving unmanageable unyielding vicious violent

arduous backbreaking baffling burdensome demanding effortful exacting exhausting exigent grievous hairy handful hard heavy intractable intricate irksome knotty labored mean no piece of cake onerous oppressive perplexing puzzling resisting severe stiff strenuous taxing thorny toilsome troublesome trying unyielding uphill weighty wicked