invulnerability vs impregnability

invulnerability and impregnability both are nouns.

Word	Noun	Adjective	Verb	Adverb
invulnerability	Yes	No	No	No
impregnability	Yes	No	No	No

As nouns, invulnerability and impregnability are synonyms defined as:

invulnerability and impregnability: having the strength to withstand attack

invulnerability (noun)	impregnability (noun)
the property of being invulnerable; the property of being incapable of being hurt (physically or emotionally)	having the strength to withstand attack
having the strength to withstand attack