(n.) One who is rigorous; -- sometimes applied to an extreme Jansenist.

Spartan Spartanic adamant adamantine astringent austere authoritarian beetle-browed black black-browed bleak cast-iron cheerless cold crabbed dark dejected demanding dismal dreary dumpish exacting exigent firm flinty forbidding frowning fundamentalist gloomy glowering glum grim grum hard hard-core hard-nosed hardy harsh hidebound immovable immutable implacable impliable inclement inelastic inexorable inflexible intransigent iron ironbound ironclad ironhanded irreconcilable lowering melancholy meticulous moodish moody mopey moping mopish morose mumpish muscle-bound obdurate obstinate orthodox procrustean purist puristic puritan puritanic relentless rigid rigorist rigoristic rigorous rock-ribbed rockbound rough rugged saturnine scowling severe sour steely stern stiff straightlaced straitlaced strict stringent stubborn sulky sullen surly tough ugly unaffected unalterable unbending unchangeable uncompromising unfriendly ungentle ungiving unmoved unrelenting unsparing unyielding