adamant

[ ad-uh-muhnt, -mant ]
/ ˈæd ə mənt, -ˌmænt /

adjective

utterly unyielding in attitude or opinion in spite of all appeals, urgings, etc.
too hard to cut, break, or pierce.

noun

any impenetrably or unyieldingly hard substance.
a legendary stone of impenetrable hardness, formerly sometimes identified with the diamond.

Origin of adamant

before 900; Middle English < Old French adamaunt < Latin adamant- (stem of adamas) hard metal (perhaps steel), diamond < Greek, equivalent to a- a-6 + -damant- verbal adjective of damân to tame, conquer; replacing Old English athamans (< Medieval Latin) and Middle English aymont < Middle French aimant < Vulgar Latin *adimant- < Latin

OTHER WORDS FROM adamant

ad·a·man·cy [ad-uh-muhn-see] /ˈæd ə mən si/, ad·a·mance, noun ad·a·mant·ly, adverb un·ad·a·mant, adjective

British Dictionary definitions for adamancy

adamant
/ (ˈædəmənt) /

adjective

unshakable in purpose, determination, or opinion; unyielding
a less common word for adamantine (def. 1)

noun

any extremely hard or apparently unbreakable substance
a legendary stone said to be impenetrable, often identified with the diamond or loadstone

Derived forms of adamant

adamantly, adverb

Word Origin for adamant

Old English: from Latin adamant-, stem of adamas, from Greek; literal meaning perhaps: unconquerable, from a- 1 + daman to tame, conquer