tough

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