adamantine

/AE1 D AH0 M AH0 N T AY0 N/
adjective
  1. 1

    Made of adamant, or having the qualities of adamant; incapable of being broken, dissolved, or penetrated.

    โ€œadamantine bondsโ€

  2. 2

    Like the diamond in hardness or luster.

Source: https://en.wiktionary.org/wiki/adamantine