In`ex·pug'na·ble adjective [ Latin inexpugnabilis : confer French inexpugnable . See In- not, and Expugnable .] Incapable of being subdued by force; impregnable; unconquerable. Burke. « A fortress, inexpugnable by the arts of war.» Milman. Found on http://www.encyclo.co.uk/webster/I/51