substratum

As nouns the difference between basement and substratum

is that basement is a floor of a building below ground level while substratum is a layer that lies underneath another.

As nouns the difference between substratum and bedrock

is that substratum is a layer that lies underneath another while bedrock is the solid rock that exists at some depth below the ground surface. Bedrock is rock "in place", as opposed to material that has been transported from another location by weathering and erosion.

As a noun substratum

is a layer that lies underneath another.

As an adjective principal is

principal, main.

In linguistics terms the difference between substratum and superstratum

is that substratum is a substrate while superstratum is a language imposed upon a population that previously spoke another language.

As nouns the difference between substratum and superstratum

is that substratum is a layer that lies underneath another while superstratum is a stratum that is on top of another.