See tenacity in Webster's New World Roget's A-Z Thesaurus II
noun
The quality or state of being stubbornly unyielding:
bullheadedness, doggedness, hardheadedness, mulishness, obstinacy, obstinateness, pertinaciousness, pertinacity, perverseness, perversity, pigheadedness, tenaciousness, willfulness. See resist
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