IPA: /ɪnˈɛkspʌɪnəblɪ/
KK: /ɪnˈɛkspʌɪnəblɪ/
In a way that cannot be overcome or defeated; impossible to capture or conquer.
The fortress stood inexpugnably against all attacks for centuries.
Inexpugnably → It is formed from "in-" (meaning not), "expugnare" (from Latin, meaning to conquer or capture), and "-ably" (meaning in a manner that can be). The word "inexpugnably" means in a manner that cannot be conquered or captured.
Think of 'not' ('in-') being able to be 'conquered' ('expugnare') — that's why inexpugnably means something that cannot be overcome.