unbreakable

/ʌnˈbreɪkəbəl/
adjective
  1. Not able to be broken; very strong or durable.
    • She bought unbreakable plates for her toddler's meals.
    • The company advertises its unbreakable phone screen as a major selling point.
    • The unbreakable bond between the two sisters lasted a lifetime.
  2. Not able to be violated or ended; permanent or absolute.
    • They made an unbreakable promise to always support each other.
    • Some traditions feel unbreakable, even as the world changes around them.
    • The treaty was meant to be an unbreakable agreement between the nations.