tough

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