Words

adamant

adamant

(ˈædəməntPronunciation for adamant)
  adjective
    1 unshakable in purpose, determination, or opinion; unyielding
    2 a less common word for adamantine (sense 1)

▷ 
noun
    3 any extremely hard or apparently unbreakable substance
    4 a legendary stone said to be impenetrable, often identified with the diamond or loadstone
  [Old English: from Latin adamant-, stem of adamas, from Greek; literal meaning perhaps: unconquerable, from a-1 + daman to tame, conquer]

ˈadamantly
adverb

adamantine

adamantine

(ˌædəˈmæntaɪnPronunciation for adamantine)
  adjective
    1 very hard; unbreakable or unyielding
    2 having the lustre of a diamond