tough

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