Undefeatability is a synonym of impregnability.
As nouns the difference between impregnability and undefeatability
is that impregnability is the quality or state of being impregnable; invincibility while undefeatability is the quality of being undefeatable; undefeatableness.
impregnability
English
Noun
(-)
The quality or state of being impregnable; invincibility.
References
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undefeatability
English
Noun
(-)
The quality of being undefeatable; undefeatableness.
Synonyms
*unbeatability
*unbeatableness
*undefeatableness (rare)
*invincibility
*invulnerability
*impregnability