Source : Webster's Revised Unabridged Dictionary (1913)

Shaster \Shas"ter\, Shastra \Shas"tra\, n. [Skr. c[=a]stra an
   order or command, a sacred book, fr. c[=a]s to order,
   instruct, govern. Cf. {Sastra}.]
   A treatise for authoritative instruction among the Hindoos; a
   book of institutes; especially, a treatise explaining the
   Vedas. [Written also {sastra}.]