inexpugnable (adj.)youdaoicibaDictYouDict[inexpugnable 词源字典]
late 15c., from Latin inexpugnabilis "not to be taken by assault," from in- "not" (see in- (1) + expuglabilis, from expugnare (see expugn).[inexpugnable etymology, inexpugnable origin, 英语词源]