1. the quality or state of being impregnable; the condition of being impossible to capture, break through, or overcome
Usage: abstract noun derived from the adjective 'impregnable'; formal register

Examples

• The fortress's impregnableness made it a symbol of military power for centuries.
• The impregnableness of their defensive position gave the soldiers confidence.
• Her logical arguments possessed an impregnableness that no opponent could challenge.
• The castle's impregnableness was tested but never broken during the siege.
• The impregnableness of the vault made it the safest place to store valuables.
• They relied on the impregnableness of their alliance to deter aggression.