Firmly, often unreasonably immovable in purpose or will:
adamant, adamantine, brassbound, die-hard, grim, implacable, inexorable, inflexible, intransigent, iron, obdurate, relentless, remorseless, rigid, stubborn, unbendable, unbending, uncompliant, uncompromising, unrelenting, unyielding. Idiom: stubborn as a mule (or ox). See resist
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