From: Marc Verhaegen
Message: 972
Date: 2000-01-18
The standard term is "substratum" or "substrate". A substrate language is what you are describing as a "submerged language". A substratum language is spoken of when a population has undergone language replacement. In ancient France, Romance replaced the Celtic language of the Gauls, but left certain remains, both in vocabulary, and in phonology. In other circumstances, even a few grammatical elements are passed on to the successor language.