tough

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