tough

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