unassailable

Adjective

• without flaws or loopholes
  • an ironclad contract
    
  • a watertight alibi
    
  • a bulletproof argument
    

• impossible to assail

• immune to attack; incapable of being tampered with
  • an impregnable fortress
    
  • fortifications that made the frontier inviolable
    
  • a secure telephone connection
    

Related words

• Synonyms: 
  unshakable , watertight , bulletproof , untouchable , impregnable , inviolable , secure , strong , unattackable