ἀδάμας

1. properly the untamed, unconquerable :

2. as Substantive adamant , i. e. the hardest metal, probably steel : metaphorically of any thing unalterable , ἔπος ἐρέω ἀδάμαντι πελάσσας having fixed it firm as adamant , (Oracle quoted in Herdotus Historicus)

3. the diamond , (Theophrastus Philosophus)

4. as adjective, metaphorically, the inflexible , of Hades, (Theocritus Poeta Bucolicus) (ML)