Synonyms and related words :
Spartan, Spartanic, adamant, adamantine, afterpart, afterpiece, arse, ascetic, ass, astringent, austere, authoritarian, back, back door, back seat, back side, backside, beam, behind, bottom, breech, bum, butt, can, cast-iron, cheeks, churlish, counter, crabbed, crabby, critical, crusty, demanding, derriere, determined, dour, exacting, exigent, fanny, fantail, firm, flinty, forbidding, frowning, gloomy, grave, grim, gruff, hard, hard-core, harsh, heel, hind end, hind part, hindhead, immovable, immutable, implacable, impliable, inclement, inelastic, inexorable, inflexible, intransigent, iron, irreconcilable, keister, lugubrious, meticulous, mortified, obdurate, occiput, poop, posterior, postern, prat, rear, rear end, rearward, relentless, resolute, reverse, rigid, rigorous, rock-ribbed, rough, rudderpost, rugged, rump, rusty-dusty, saturnine, serious, severe, sour, steadfast, steely, stiff, stony, strict, stringent, taciturn, tail, tail end, tailpiece, tough, tuchis, tush, tushy, unaffected, unalterable, unbending, unchangeable, uncompromising, unforgiving, ungentle, ungiving, unmoved, unrelenting, unremitting, unsparing, unsympathetic, unyielding