Undecorous means lacking in good taste or inappropriate. Some antonyms for undecorous are appropriate, tasteful, elegant, refined, polished, sophisticated, graceful, and cultured. Choosing antonyms for "more undecorous" will depend on the context and purpose of the sentence. For instance, in a formal setting, "appropriate" or "tasteful" might be good antonyms. On the other hand, "sophisticated" or "cultured" might be appropriate antonyms in a discussion on aesthetics or art. Whatever the situation, antonyms for "more undecorous" can provide an excellent opportunity to improve the quality of the language by offering more precise and concise alternatives.