The Collaborative International Dictionary of English v.0.48:

Apophasis \A*poph"a*sis\ ([.a]*p[o^]f"[.a]*s[i^]s), n. [Gr.
   'apo`fasis denial, fr. 'apofa`nai to speak out, to deny.]
   (Rhet.)
   A figure by which a speaker formally declines to take notice
   of a favorable point, but in such a manner as to produce the
   effect desired. [For example, see Mark Antony's oration.
   --Shak., Julius C[ae]sar, iii. 2.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

apophasis
    n 1: mentioning something by saying it will not be mentioned