The Collaborative International Dictionary of English v.0.48:

Prolegomenon \Prol`e*gom"e*non\, n.; pl. Prolegomena. [ NL.,
   fr. Gr. ?, properly neut. pass. p. pr. of ? to say
   beforehand; ? before + ? to say.]
   A preliminary remark or observation; an introductory
   discourse prefixed to a book or treatise. --D. Stokes (1659).
   Sir W. Scott.
   [1913 Webster]