tough

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