The word "superstructural" refers to something that is above or complementary to a basic structure or foundation. Synonyms for this word could include words like supplementary, additional, adjunct, ancillary, or secondary. These words all convey the sense of being an extra layer or support to the core foundation of something. Other synonyms for "superstructural" might include words like ornamental, decorative, or embellishing, which imply an aesthetic or decorative function rather than a functional or structural one. Overall, the synonyms for "superstructural" capture the sense of adding something extra or enhancing an existing structure or system.