Ruthenian
Ruthenian language, also known as Rusian (or less precisely as Russian), was a Slavic language spoken in Ruthenia or Rus' from about 800 to 1200 AD. The oldest known texts in Ruthenian were written in the 10th century.From the Ruthenian language, the following languages evolved: Ukrainian, Belarusian, and together with Old Church Slavonic, the Russian language.
The Rusyn language is also sometimes referred to as Ruthenian. However, most Slavic linguists do not recognize it as a distinct language and consider the Carpatho-Ruthenian dialects as regional versions of Ukrainian.