noun
diachronic linguistics
Technical term in linguistics for the study of language change over time, often contrasted with 共時言語学 (synchronic linguistics).
通時言語学は、言語の歴史的変化を研究する分野です。
Diachronic linguistics is the field that studies historical changes in language.
共時言語学 studies language at a single point in time, while 通時言語学 examines how language evolves over time.
Compound of 通時 (diachronic) + 言語学 (linguistics). The term is a calque from Western linguistics.