tough

adamant aggressive arduous awful bad brawny brawnier bully bullies burdensome callous chewy conscientious courageous crabbiest crabbiest crabby/crabbed crabby crabbier crabbier 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 hard-nosed/hardheaded harsh harsher harshest healthy healthiest heaviest heavy Herculean high-grade hood incompressible incompliant insensitive insusceptible intimidator intractable intractable/intransigent kinetic laborious knotty knockabout leathery lusty malevolent more intransigent more intractable more intractable more efficient more aggressive more hardnosed more hardnosed more hard nosed more hard nosed more durable more hard-nosed more hard-nosed more difficult more difficult more demanding more crabbed more hardheaded more hardheaded more robust more stringent more thoroughgoing more serious more primary more thorough most crabbed most awful most efficient most hardnosed most hardnosed most hardheaded most hardheaded most hard nosed most hard nosed most hard-nosed most hard-nosed most intransigent most intractable most intractable most primary most serious most robust most thoroughgoing most thorough mucilaginous muscular nasty naughty obdurate oppressive particular praiseworthy primest primary/prime prisoner prisoners puissant rascal remorseless resilient reusable rocky robust roughest rough rougher rough-and-tumble roughneck rugged rugged serious severe spunky stable stalwart staunchest staunch stern stony stiff stouter stout strenuous strict stringent stricter strictest 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 uphill unsympathetic unyielding vigorous valorous vicious viscid viscose viscous weighty wiry