Rigorous

Adjective

 * 1) Manifesting, exercising, or favoring rigor; allowing no abatement or mitigation; scrupulously accurate; exact; strict; severe; relentless; as, a rigorous officer of justice; a rigorous execution of law; a rigorous definition or demonstration.
 * 2) Severe; intense; inclement; as, a rigorous winter.
 * 3) Violent.

Thesaurus
Herculean, Siberian, abstruse, accurate, acid, acidulous, acrid, acrimonious, acute, adamant, adamantine, adverse, algid, antagonistic, arctic, arduous, ascetic, astringent, attentive, below zero, biting, bitter, bitterly cold, bleak, boreal, brisk, brumal, brutal, burdensome, cast-iron, caustic, close, cold, cold as charity, cold as death, cold as ice, cold as marble, complex, conflicting, conscientious, constant, contrary, correct, counter, counteractive, crisp, critical, cutting, delicate, demanding, detailed, detrimental, difficile, difficult, direct, double-edged, dour, draconian, drastic, edged, escharotic, even, exact, exacting, excessive, exigent, exorbitant, express, exquisite, extravagant, extreme, faithful, fierce, fine, finical, finicking, finicky, firm, flinty, formidable, freezing, freezing cold, frigid, fundamentalist, furious, fussy, gelid, glacial, great, grim, hairy, hard, hard-core, hard-earned, hard-fought, harmful, harsh, hibernal, hidebound, hiemal, hostile, hyperborean, ice-cold, ice-encrusted, icelike, icy, immoderate, immovable, immutable, implacable, impliable, in opposition, incisive, inclement, inelastic, inerrable, inerrant, inexorable, infallible, inflexible, inimical, intemperate, intense, intransigent, intricate, iron, ironbound, ironclad, ironhanded, irreconcilable, jawbreaking, keen, knotted, knotty, laborious, mathematical, mean, meticulous, micrometrically precise, microscopic, minute, miserable, mordacious, mordant, muscle-bound, narrow, nice, nipping, nippy, no picnic, not easy, numbing, obdurate, obstinate, onerous, operose, opposed, opposing, opposite, oppressive, orthodox, outrageous, particular, penetrating, piercing, pinching, pinpoint, poignant, precise, precisianistic, precisionistic, procrustean, proper, punctilious, punctual, purist, puristic, puritan, puritanic, raw, refined, relentless, religious, religiously exact, right, rigid, rigorist, rigoristic, rock-ribbed, rockbound, rough, rugged, scathing, scientific, scientifically exact, scrupulous, scrutinizing, set with thorns, severe, sharp, sinister, sleety, slushy, snappy, spiny, splitting, square, stabbing, steely, steep, stern, stiff, stinging, stone-cold, straightlaced, straitlaced, strenuous, stressful, strict, strident, stringent, stubborn, subtle, subzero, supercooled, tart, thorny, ticklish, toilsome, tough, trenchant, tricky, troublesome, troublous, trying, unaffected, unalterable, unbending, unchangeable, uncompromising, unconscionable, undeviating, unerring, unfavorable, ungiving, unmoved, unrelenting, untoward, unyielding, uphill, vehement, venomous, violent, virulent, vitriolic, wicked, winterbound, winterlike, wintery, wintry, wretched