Antonyms for the word "castle in air" include terms like realistic, practical, achievable, possible, tangible, and materialistic. These terms correspond to the idea of something that is grounded in reality, rather than purely imaginary. While building castles in the air may represent a form of dreaming or fantasizing, the antonyms for this phrase suggest a more productive approach. By putting one's energy and focus on achievable goals, rather than unrealistic or unrealistic ideas, individuals are more likely to achieve their desired outcomes. Thus, the antonyms for "castle in air" suggest a more pragmatic and sensible mindset, which is essential for success in both personal and professional realms.