substratum

(noun) a surface on which an organism grows or is attached. Synonyms: substrate. Example: "The gardener talked about the proper substrate for acid-loving plants."

(noun) any stratum or layer lying underneath another. Synonyms: substrate.

(noun) an indigenous language that contributes features to the language of an invading people who impose their language on the indigenous population. Synonyms: substrate. Example: "The celtic languages of britain are a substrate for english."