Substructures refer to the underlying support system of different architectural and engineering projects. Antonyms of substructures are elements that are not below the surface, but rather reside atop or above other structures. For example, superstructure is the opposite of substructures. Superstructures refer to the upper portion of a building or a ship, visible above the waterline. Other antonyms might include surface, exterior, or shell. All of these words indicate that there is nothing underneath them, unlike substructures that are the foundation of the structure. While substructures are essential for stability and strength, antonyms provide a contrast to the underlying framework, creating the visible aspect of the structure.