I. ˈa-də-mənt, -ˌmant noun
Etymology: Middle English, from Anglo-French, from Latin adamant-, adamas hardest metal, diamond, from Greek
Date: 14th century
1. : a stone (as a diamond) formerly believed to be of impenetrable hardness
2. : an unbreakable or extremely hard substance
II. adjective
Date: 1897
: unshakable or insistent especially in maintaining a position or opinion : unyielding
Synonyms: see inflexible
• ad·a·mant·ly adverb