The antonyms for the word "more undefinable" are "clear", "certain", "definite", "exact", "explicit", "precise", "unambiguous", "well-defined", "plain", and "distinct". These terms refer to concepts that are easily comprehensible, defined, and can be easily articulated. The antonyms of "more undefinable" are significant in communicating messages because it provides clarity and removes ambiguity in communication. By using antonyms, people can express their thoughts, ideas, and feelings more accurately and effectively. It is essential to understand the use of antonyms in communication to enhance understanding and avoid misunderstandings that could lead to conflicts.