tough

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