Adamant means refusing absolutely to change your mind. Adamant that he was right, remain adamant, adamantly opposed.
It is stronger than firm and implies immovability rather than mere conviction. It takes that or about — adamant that it happened, adamant about the price. Note adamantly; and that the word once named the hardest substance imaginable, from a Greek word meaning unconquerable — which is also where diamond comes from, so adamant and diamond are the same word.
1adjectiveadamantRefusing absolutely to change your mind.
“She was adamant that she had locked the door, even though it was wide open.”
synonyms: unyielding, resolute
adamant is a quality of firmness.
Greek adamas means invincible, from a- plus daman, to tame. It named the hardest known substance, and diamond is the same word arriving through Latin and French.
Ancient Greek
ἀδάμας — invincible
Latin
adamantem
Middle English
adamant
English, today
adamant
Built from
From Middle English adamant, adamaunt, from Latin adamantem, accusative singular form of adamās (“hard as steel”), from Ancient Greek ἀδάμας (“invincible”), oblique stem of ἀδάμας. a doublet of diamond.
Etymology from Wiktionary, CC BY-SA