tough

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