The Collaborative International Dictionary of English v.0.48:

Prefatory \Pref"a*to*ry\, a.
   Pertaining to, or of the nature of, a preface; introductory
   to a book, essay, or discourse; as, prefatory remarks.
   [1913 Webster]

         That prefatory addition to the Creed.    --Dryden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

prefatory
    adj 1: serving as an introduction or preface [syn:
           introductory, prefatorial, prefatory]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "prefatory":
   antecedent, anterior, chief, exordial, first, foremost, headmost,
   inaugural, inductive, initiatory, introductory, leading, opening,
   precedent, preceding, precessional, precursory, prefixed, prelim,
   preliminary, preludial, prelusive, preparatory, prepositive,
   prevenient, prior, proemial, propaedeutic