Source : Webster's Revised Unabridged Dictionary (1913)

Avestan \A*ves"tan\, a.
   Of or pertaining to the Avesta or the language of the Avesta.
   -- n. The language of the Avesta; -- less properly called
   {Zend}.

Source : WordNet®

Avestan
     adj : of or pertaining to the Avesta (sacred text of
           Zoroastrianism)
     n 1: an ancient Iranian language [syn: {Zend}]
     2: the script in which the ancient Persian language of the
        Avesta is written