Synonyms to hard core

adamant, adamantine, ardent, cast-iron, dour, fanatic, fiery, firm, flaming, flinty, grim, hard, heated, hot, hotheaded, immovable, immutable, implacable, impliable, inelastic, inexorable, inflamed, inflexible, intransigent, iron, irreconcilable, madcap, passionate, red-hot, relentless, rigid, rigorous, rock-ribbed, scorching, steely, stern, stiff, totally committed, unaffected, unalterable, unbending, unchangeable, uncompromising, ungiving, unmoved, unrelenting, unyielding, white-hot, zealous