1. an underlying layer or substance
2. a basis or foundation underlying something
Usage: often used figuratively
3. a layer of rock or soil beneath the surface layer
Usage: geological

Examples

• The archaeologists discovered artifacts in the clay substratum beneath the site.
• There was a substratum of truth in his seemingly wild accusations.
• The building’s foundation was anchored in the rocky substratum.
• Cultural traditions form the substratum of social behavior.
• Geologists studied the limestone substratum under the valley.
• The substratum of her argument was based on solid research.
• Workers had to dig through several layers to reach the substratum.