The word Iran

According to the Zend Avesta, the Airyanem Vaejah was "by the Vanguhi Daitya".  In the Middle Ages this river was called Veh, which was the Oxus.  Since according to Fargard 1, the second to the fifth "perfect lands created by Ahura Mazda"  (Sogdiana, Margiana, Bactria, and "Nisaya" between Margiana and Bactria) were located by the Oxus, it is reasonable to assume that the first one, Airyanem Vaejah, was also.  The region of present-day Turkmenistan would be a most likely place.  Hence the term Airyanem (or its Old Persian equivalent?) migrated further south into Iran.