The word "more undefendable" indicates something that is even more weak and unable to be protected. Its antonym, therefore, would be something that is strong and easily defendable. Words such as defensible, secure, fortified, and protected can be used as antonyms for more undefendable. Furthermore, synonyms of these antonyms include impregnable, invulnerable, unassailable, and guarded. When it comes to defense, choosing the right words to convey the message is essential. By using the correct antonyms, writers can effectively convey their message while ensuring they are clear and accurate.