adjective (a)

• not subject or susceptible to change or variation in form or quality or nature(adj.all)

  Example:
  The view of that time was that all species were immutable, created by God.
  

  Synonym:
  changeless
  Antonym:
  changeable, mutable
  

  source: wordnet30
• Not mutable; not capable or susceptible of change; unchangeable; unalterable.(adjective)

  source: webster1913