substratum

What it means

1. A layer that lies underneath another.

   ..; in this case it became necessary to employ a machine like the lapidary's wheel, partially to grind away the colored surface till the white substratum appeared.

   1847, editorial staff, “Painting on Glass”, in Scientific American, series 1, Volume 3, Issue 9, page 72

   Synonyms: underlayer

2. figurativelyThe underlying cause or basis of something.

   However exaggerated an estimate this might be, the substratum of truth was solid and auriferous enough to dazzle the imagination.

   1914, Ernest Bramah [pseudonym; Ernest Brammah Smith], Max Carrados

3. human sciencesA substrate.

In a sentence

..; in this case it became necessary to employ a machine like the lapidary's wheel, partially to grind away the colored surface till the white substratum appeared.

1847, editorial staff, “Painting on Glass”, in Scientific American, series 1, Volume 3, Issue 9, page 72

Where it comes from

1. Latinsubstrātus
2. New Latinsubstrātum
3. Englishsubstratum

Learned borrowing from New Latin substrātum, nominalisation of the neuter of Latin substrātus, perfect passive participle of substernō. By surface analysis, sub- + stratum.