adamantine

Adjective

• impervious to pleas, persuasion, requests, reason; she would have none of him"- W.Churchill
  • he is adamant in his refusal to change his mind
    
  • Cynthia was inexorable
    
  • an intransigent conservative opposed to every liberal tendency
    

• having the hardness of a diamond

• consisting of or having the hardness of adamant

Related words

• Synonyms: 
  adamant , inexorable , intransigent