Superstratum is a term used to describe the uppermost layer of something, and it is often associated with geology, archaeology, and linguistics. The concept of superstratum is closely related to that of substratum, which refers to the underlying layer of something. Therefore, some antonyms for superstratum include substratum, base, foundation, bedrock, and bottom. These words describe the lowermost layer or the fundamental support of a particular structure. Another possible antonym for superstratum is the term "inferior layer," which emphasizes the idea of lower quality or a lesser degree of importance. Overall, antonyms for superstratum highlight the contrast between the topmost layer and the layers beneath it.