Bactrian

Bactrian, a term now commonly used as a substitute for Zend, to indicate the eastern branch of the old Iranian language at one time current throughout Bactria, a province of the ancient Persian empire; two varieties: Gatha of the oldest Gathas (hymns) attributed to Zarathrastra (Zoroaster); and Avesta, for many centuries current in East Irania, died out about the 4th century B.C.