tough

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