substratum

In linguistics, a stratum (Latin for 'layer') or strate is a historical layer of language that influences or is influenced by another language through contact. The notion of "strata" was first developed by the Italian linguist Graziadio Isaia Ascoli, and became known in the English-speaking world through the work of two different authors in 1932.

Both concepts apply to a situation where an intrusive language establishes itself in the territory of another, typically as the result of migration. Whether the superstratum case (the local language persists and the intrusive language disappears) or the substratum one (the local language disappears and the intrusive language persists) applies will normally only be evident after several generations, during which the intrusive language exists within a diaspora culture.