tough

adamant aggressive arduous awful bad brawny brawnier bullies burdensome bully callous chewy conscientious courageous crabby crabby/crabbed crabbier crabbier crabbiest crabbiest demanding difficult difficult dispassionate durable efficient effortful energetic exacting exigent feisty firm formidable forbidding gangster glutinous grievous gritty hard hard hard hardheaded harder harder harder hard-nosed/hardheaded hard-nosed harshest harsher harsh healthiest healthy heaviest heavy Herculean high-grade hood incompliant incompressible insensitive insusceptible intractable/intransigent intractable intimidator kinetic knockabout knotty laborious leathery lusty malevolent more intransigent more intractable more intractable more hardnosed more hardnosed more aggressive more hard nosed more hard nosed more efficient more hard-nosed more hard-nosed more durable more difficult more difficult more demanding more crabbed more hardheaded more hardheaded more stringent more robust more thoroughgoing more serious more thorough more primary most awful most hardnosed most hardnosed most crabbed most efficient most hardheaded most hardheaded most hard-nosed most hard-nosed most hard nosed most hard nosed most intransigent most intractable most intractable most robust most serious most primary most thoroughgoing nasty most thorough mucilaginous muscular naughty obdurate oppressive particular praiseworthy primary/prime primest prisoners prisoner puissant rascal remorseless resilient reusable rocky robust rough roughest rough-and-tumble rougher roughneck rugged rugged serious severe spunky stable stalwart staunch staunchest stiff stern stouter stout stony strict stricter strictest strenuous stringy stringent stubborn strong strong strong sturdy tenacious taxing thick-skinned thoroughpaced thorough/thoroughgoing thorny tighter tightest tight tiresome troublesome trying tyrannical unbendable uncompliant uncompromising uncompassionate unfeeling unhospitable unpitying unrelenting unsavory unstirred uphill unsympathetic unyielding vigorous valorous vicious viscid viscose viscous weighty wiry