The Collaborative International Dictionary of English v.0.48:

Pehlevi \Peh"le*vi`\, n. [Parsee Pahlavi.]
   An ancient Persian dialect in which words were partly
   represented by their Semitic equivalents. It was in use from
   the 3d century (and perhaps earlier) to the middle of the 7th
   century, and later in religious writings. [Written also
   Pahlavi.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

Pehlevi
    n 1: the Iranian language of the Zoroastrian literature of the
         3rd to 10th centuries [syn: Pahlavi, Pehlevi]