Avesta

[Short for ZEND-AVESTA.]

The Avesta is the Bible of Zoroastrianism (see Zoroastrian entries). Most of the original Avesta, much of which predates the Zoroastrian reforms of the old Iranian religion (see Aryans) has been lost. The most important part of the Avesta is the Yasna (“Sacrifice,” related to the Hindu Yajna), verses meant to be used by priests during sacrifice rituals. Contained in the Yasna are the Gāthās, “songs” said to have been written by Zarathustra (see Zoroaster), containing the essence of the prophet's philosophy. Also important in the Avesta are the Yashts, hymns that tell us much of what we know of Zoroastrian mythology.

The noun has one meaning:

Meaning #1: sacred text of Zoroastrianism
  Synonym: Zend-Avesta