The Collaborative International Dictionary of English v.0.48:

Mishna \Mish"na\, n. [NHeb. mishn[=a]h, i. e., repetition,
   doubling, explanation (of the divine law), fr. Heb.
   sh[=a]n[=a]h to change, to repeat.]
   A collection or digest of Jewish traditions and explanations
   of Scripture, forming the text of the Talmud. [Written also
   Mischna.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

Mishna
    n 1: the first part of the Talmud; a collection of early oral
         interpretations of the scriptures that was compiled about
         AD 200 [syn: Mishna, Mishnah]