Authoritarian, Back, Backside, Beam, Behind, Bottom, Breech, Bum, Butt, Can, Cheeks, Churlish, Counter, Crabby, Critical, Crusty, Demanding, Determined, Dour, Exacting, Exigent, Fanny, Fantail, Firm, Flinty, Forbidding, Frowning, Gloomy, Grave, Grim, Gruff, Hard, Harsh, Heel, Immovable, Immutable, Implacable, Inclement, Inelastic, Inexorable, Inflexible, Intransigent, Iron, Irreconcilable, Lugubrious, Meticulous, Mortified, Obdurate, Poop, Posterior, Prat, Rear, Rearward, Relentless, Resolute, Reverse, Rigid, Rigorous, Rough, Rugged, Rump, Saturnine, Serious, Severe, Sour, Steadfast, Steely, Stiff, Stony, Strict, Stringent, Taciturn, Tail, Tailpiece, Tough, Unaffected, Unalterable, Unbending, Unchangeable, Uncompromising, Unforgiving, Unmoved, Unrelenting, Unremitting, Unsympathetic, Unyielding, Spartan, Adamant, Ascetic, Ass, Astringent, Austere