Lewis & Short

† ădămas, antis, m. (acc. Gr. adamanta, adamantas), = ἀδάμας (invincible),

  1. I. adamant, the hard est iron or steel; hence poet., for any thing inflexible, firm, lasting, etc. (first used by Verg.): porta adversa ingens solidoque adamante columnae, Verg. A. 6, 552; cf. Mart. 5, 11; adamante texto vincire, with adamantine chains, Sen. Herc. F. 807.
    Trop. of character, hard, unyielding, inexorable: nec rigidos silices solidumve in pectore ferrum aut adamanta gerit, a heart of stone, Ov. M. 9, 615: lacrimis adamanta movebis, will move a heart of stone, id. A. A. 1, 659; so id. Tr. 4, 8, 45: voce tua posses adamanta movere, Mart. 7, 99: duro nec enim ex adamante creati, Sed tua turba sumus, Stat. S. 1, 2, 69.
  2. II. The diamond: adamanta infragilem omni cetera vi sanguine hireino rumpente, Plin. 20, prooem. 1; 37, 4, 15, § 55 sq.