tough

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