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/hardheaded harder harder harder hard-nosed harsh harsher healthiest healthy heavy heaviest Herculean high-grade hood incompliant incompressible insensitive insusceptible intractable/intransigent intractable intimidator kinetic knockabout knotty laborious leathery lusty malevolent more durable more crabbed more demanding more efficient more aggressive more difficult more difficult more hardnosed more hardnosed more hardheaded more hardheaded more hard-nosed more hard-nosed more hard nosed more hard nosed more intransigent more intractable more intractable more primary more serious more thorough more thoroughgoing more stringent more robust most awful most crabbed most efficient most hard-nosed most hard-nosed most hardnosed most hardnosed most hard nosed most hard nosed most hardheaded most hardheaded most intractable most intractable most intransigent 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-and-tumble rougher roughneck rough roughest rugged rugged serious severe spunky stable stalwart staunchest staunch stern stiff stony stouter stout strenuous strict stricter strictest stringy stringent strong strong strong stubborn sturdy taxing tenacious thick-skinned thorny thorough/thoroughgoing thoroughpaced tightest tight tighter tiresome troublesome trying tyrannical unbendable uncompassionate uncompliant uncompromising unfeeling unhospitable unpitying unrelenting unsavory unstirred unsympathetic unyielding uphill valorous vicious vigorous viscid viscous viscose weighty wiry