tough

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