The Collaborative International Dictionary of English v.0.48:

Lipogram \Lip"o*gram\ (l[i^]p"[-o]*gr[a^]m; 277), n. [Gr.
   lei`pein, lipei^n, to leave, omit + -gram.]
   A writing composed of words not having a certain letter or
   letters; -- as in the Odyssey of Tryphiodorus there was no A
   in the first book, no B in the second, and so on.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lipogram
    n 1: a text that excludes a particular letter or particular
         letters of the alphabet