Firmly, often unreasonably immovable in purpose or will:
adamant, adamantine, 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 resistLearn more about brassbound