Philology - the branch of knowledge that deals with the structure, historical development, and relationships of a language or languages
Historical-Comparative Linguistics - branch of historical linguistics that is concerned with comparing languages to establish their historical relatedness
Terminology
glottochronology - the use of statistical data to date the divergence of languages from their common sources
proto-language - proto- meaning first. an idea that all existing languages come from a common “proto-language”