unshakable

Adjective

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

• marked by firm determination or resolution; not shakable
  • firm convictions
    
  • a firm mouth
    
  • steadfast resolve
    
  • a man of unbendable perseverence
    
  • unwavering loyalty
    

Related words

• Synonyms: 
  unassailable , watertight , bulletproof , firm , steadfast , steady , stiff , unbendable , unfaltering , unwavering