Conventionally, Iranian languages are grouped in "western" and "eastern" branches. These terms have little meaning with respect to Old <answer>Avestan</answer> as that stage of the language may predate the settling of the Iranian peoples into western and eastern groups. The geographic terms also have little meaning when applied to Younger <answer>Avestan</answer> since it isn't known where that dialect (or dialects) was spoken either. Certain is only that <answer>Avestan</answer> (all forms) and Old Persian are distinct, and since Old Persian is "western", and <answer>Avestan</answer> was not Old Persian, <answer>Avestan</answer> acquired a default assignment to "eastern". Confusing the issue is the introduction of a western Iranian substrate in later <answer>Avestan</answer> compositions and redactions undertaken at the centers of imperial power in western Iran (either in the south-west in Persia, or in the north-west in Nisa/Parthia and Ecbatana/Media).
Which language is associated with the eastern branch of Iranian?
Avestan