substratum

definition: an indigenous language that contributes features to the language of an invading people who impose their language on the indigenous population
example:
speech part: noun
synonyms: substrate
definition: any stratum or layer lying underneath another
example:
speech part: noun
synonyms: substrate
definition: a surface on which an organism grows or is attached
example:
speech part: noun
synonyms: substrate

How substratum is being used?