adamant
ˈadəm(ə)nt/
adjective
adjective: adamant
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1.refusing to be persuaded or to change one’s mind.“he is adamant that he is not going to resign”
synonyms: unshakeable, immovable, inflexible, unwavering, uncompromising,resolute, resolved, determined, firm, rigid, steadfast; More antonyms: unsure
noun
archaic
noun: adamant
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1.a legendary rock or mineral to which many properties were attributed, formerly associated with diamond or lodestone.
Origin
Old English (as a noun), from Old French adamaunt-, via Latin from Greek adamas,adamant-, ‘untameable, invincible’ (later used to denote the hardest metal or stone, hence diamond), from a- ‘not’ + daman ‘to tame’. The phrase to be adamant dates from the 1930s, although adjectival use had been implied in such collocations as ‘an adamant heart’ since the 16th century.
How my heart sings 