The Collaborative International Dictionary of English v.0.48:

Frontispiece \Fron"tis*piece\, n. [F. frontispice, LL.
   frontispicium beginning, front of a church, fr. L. frons
   front + spicere, specere, to look at, view: cf. It.
   frontispizio. See Front and Spy.]
   The part which first meets the eye; as:
   (a) (Arch.) The principal front of a building. [Obs. or R.]
   (b) An ornamental figure or illustration fronting the first
       page, or titlepage, of a book; formerly, the titlepage
       itself.
       [1913 Webster]

WordNet (r) 3.0 (2006):

frontispiece
    n 1: an ornamental facade
    2: front illustration facing the title page of a book

Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "frontispiece":
   anteriority, avant-propos, bold front, brave face, brave front,
   breakthrough, display, exordium, facade, face, facet, facia, fore,
   forefront, foreground, forehand, foreland, forepart, forequarter,
   foreside, foreword, front, front elevation, front man,
   front matter, front page, front view, frontage, frontal, frontier,
   head, heading, innovation, introduction, lap, leap, obverse,
   overture, postulate, preamble, preface, prefix, prefixture,
   preliminary, prelude, premise, presupposition, priority, proem,
   prolegomena, prolegomenon, prolepsis, prologue, proscenium,
   protasis, verse, voluntary, window dressing