The Collaborative International Dictionary of English v.0.48:

Zend \Zend\, n. [See Zend-Avesta.]
   Properly, the translation and exposition in the Huzv[^a]resh,
   or literary Pehlevi, language, of the Avesta, the Zoroastrian
   sacred writings; as commonly used, the language (an ancient
   Persian dialect) in which the Avesta is written.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Avestan \A*ves"tan\, a.
   Of or pertaining to the Avesta or the language of the Avesta.
   -- n. The language of the Avesta (an ancient Iranian
   language); -- less properly called Zend.

   Syn: Zend
        [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

Zend
    n 1: an ancient Iranian language [syn: Avestan, Zend]