tough

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