The term un-functional refers to something that does not work or operate correctly, usually due to some kind of defect or malfunction. In contrast, antonyms for un-functional are functional, operative, working, efficient, effective, and reliable. These words denote an object or system that is in good working order, performs its intended task as expected, and does so consistently over time. A functional object is one that is useful, practical, and serves its intended purpose without any problems. Therefore, when describing something as un-functional, it is important to understand the antonyms in order to indicate its opposite and provide a clear contrast.