Proto-Yeniseian refers to the hypothetical ancestor language that gave rise to the Yeniseian language family, spoken in central Siberia. Synonyms for the term Proto-Yeniseian include the Proto-Eniseian language, the ancestral Yeniseian language, and the prehistoric Yeniseian language. The term 'proto-' is often used in linguistics to refer to a reconstructed ancient language, and in the case of Proto-Yeniseian, it is used to describe the language that is believed to have been spoken by the common ancestors of all modern-day Yeniseian languages. While our knowledge of Proto-Yeniseian is limited, comparative linguistic research has enabled us to reconstruct some features and vocabulary of this ancestral language.