Synonyms of adamantine

1 Syllable
hard, firm, mule
2 Syllables
hardest, steely, irons, mulish, harder, steelier, steeler, rigid, ferrous, iron, brass-bound, brassbound, ferric
3 Syllables
uncompliant, unyielding, hard-handed, hardheaded, adamant, pigheaded, incompliant, shatterproof, relentless, unbending, hard-bitten
4 Syllables
unbreakable, remorseless, implacable, intransigent, obdurate, unrelenting, obstinate, inflexible, unbendable, infrangible, nonbreakable, singleminded, diamondlike
5 Syllables
uncompromising, inalterable, inexorable, unadaptable, opinionated, unpermissive, diamondiferous