In linguistics, a substratum is a language which influences another one while that second language supplants it. It is one of three possible types of linguistic interference.

A language, "A", occupies a given territory. A language, "B" (brought, for example, with migrations of population) arrives in the territory. It makes contact, and then interferes with language A. Language B is going to supplant language A: the speakers of language A abandon their own language in favour of that of population B, generally because they believe that it is in their best interests (economic, political, cultural, social). Nevertheless, language A influences language B, even if only because the speakers retain certain features characteristic of their former language.

For example, Gaulish is a substratum of French. A Celtic people, the Gauls, lived in the current French-speaking territory before the arrival of the Romans. Given the cultural, economic and political prestige which Latin enjoyed, the Gauls eventually abandoned their language in favour of Latin, which evolved in this region until eventually it took the form of Modern French. The Gaulish speech disappeared, but it remains detectable in some French words (approximately ninety).

Linguistic substrata are often difficult to detect, especially when the substratum language and its nearest relatives are extinct. There are many controversial theories related to linguistic substrata. For instance, some linguists contend that Japanese consists of an Altaic superstrate projected onto an Austronesian or Sinitic substrate, or alternatively that it consists of a Korean superstrate projected onto an indigenous isolated substrate.

It has also been proposed, controversially, that the Germanic languages arose as a result of the projection of an Indo-European language (most probably a Celtic or Slavic language) onto a Finno-Ugric or Afro-Asiatic substratum. This conjecture has been offered as an explanation of the cryptic, apparently non-Indo-European origin of many Germanic roots. See, Germanic substrate hypothesis.

In horticulture: materials allowing the binding of roots of a plant.

See also

• Linguistic interference
• Superstratum
• Adstratum (?)