tough

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