ădămantĭnus

I. hard as steel, etc., adamantine: saxa, Lucr. 2, 447: duritia, Plin. 37, 11, 73. —Hence poet., extremely hard, inflexible, invincible: clavi, Hor. C. 3, 24, 5: tunica, id. ib. 1, 6, 13: juga, Prop. 3, 9, 9; cf. aënus.