impregnableness

/ɪmˈprɛɡnəbəlnəs/
noun
  1. The quality of being impossible to capture, defeat, or overcome; invincibility.
    • The fortress's impregnableness made it a legend among military strategists.
    • Her argument had an impregnableness that left no room for doubt.
    • The team's defense showed remarkable impregnableness throughout the tournament.