unshakable in WordNet English dictionary

1. without flaws or loopholes
   "an ironclad contract"; "a watertight alibi"; "a bulletproof argument"
   unassailable  unshakable  watertight  bulletproof 
   
2. marked by firm determination or resolution; not shakable
   "firm convictions"; "a firm mouth"; "steadfast resolve"; "a man of unbendable perseverence"; "unwavering loyalty"
   firm  steadfast  steady  stiff  unbendable  unfaltering  unshakable  unwavering