The concept of a "concrete idea" implies a specific and tangible thought. However, it is important to understand the various antonyms that can exist for such an idea. One antonym may be an "abstract idea," which refers to a thought or concept that is not physical or concrete. Another antonym may be a "vague idea," which means a thought or concept that is unclear or fuzzy in nature. Similarly, a "general idea" may refer to a broad concept that is not specific or concrete. Finally, an "imprecise idea" may refer to a thought or concept that lacks accuracy or precision. Understanding the different antonyms for the term "concrete idea" can help in conveying meaning more effectively.