unshakable
adjective /ʌnˈʃeɪkəbl/
  /ʌnˈʃeɪkəbl/
(also unshakeable)
 - (of a feeling or an attitude) that cannot be changed or destroyed synonym firm
- unshakable loyalty
 - Their confidence in the plan appears unshakable.
 - She has an unshakable belief in the goodness of humanity.
 - They have an unshakable conviction that what they are doing is right.
 
Oxford Collocations DictionaryUnshakable is used with these nouns:- belief
 - confidence
 - conviction
 - …