noun
Linguistics term for a language that influences a later dominant language, leaving traces in vocabulary, phonology, or grammar.
フランス語にはガリア語の基層語の影響が残っている。
French retains influences from the Gaulish substratum.
Adstratum: a language that influences another through prolonged contact without clear dominance.
Compound of 基層 (base layer) + 語 (language), calque of English substratum/substrate.