See adamant in Webster's New World Roget's A-Z Thesaurus II
adjective
Firmly, often unreasonably immovable in purpose or will:
adamantine, brassbound, die-hard, grim, implacable, incompliant, inexorable, inflexible, intransigent, iron, obdurate, relentless, remorseless, rigid, stubborn, unbendable, unbending, uncompliant, uncompromising, unrelenting, unyielding. Idiom: stubborn as a mule (or ox). See resist
Learn more about adamant