IPA: /ɪmˈprɛɡnəblnəs/
KK: /ɪmˈprɛɡnəblnəs/
The quality of being impossible to penetrate or break into; the state of being secure or invulnerable.
The impregnableness of the fortress made it a safe haven during the war.
Impregnableness is formed from "impregnable" (from Latin "impregnabilis", meaning not able to be taken) and the suffix "-ness" (meaning the state or quality of). The word refers to the quality of being unable to be captured or overcome.
Think of something that cannot be taken or captured ('impregnable') and remember that '-ness' indicates a state or quality. This helps you remember that 'impregnableness' refers to the quality of being unassailable.