tough

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