The Collaborative International Dictionary of English v.0.48:

Amplification \Am`pli*fi*ca"tion\, n. [L. amplificatio.]
   1. The act of amplifying or enlarging in dimensions;
      enlargement; extension.
      [1913 Webster]

   2. (Rhet.) The enlarging of a simple statement by
      particularity of description, the use of epithets, etc.,
      for rhetorical effect; diffuse narrative or description,
      or a dilating upon all the particulars of a subject.
      [1913 Webster]

            Exaggeration is a species of amplification. --Brande
                                                  & C.
      [1913 Webster]

            I shall summarily, without any amplification at all,
            show in what manner defects have been supplied.
                                                  --Sir J.
                                                  Davies.
      [1913 Webster]

   3. The matter by which a statement is amplified; as, the
      subject was presented without amplifications.
      [1913 Webster]

WordNet (r) 3.0 (2006):

amplification
    n 1: addition of extra material or illustration or clarifying
         detail; "a few remarks added in amplification and defense";
         "an elaboration of the sketch followed" [syn:
         amplification, elaboration]
    2: the amount of increase in signal power or voltage or current
       expressed as the ratio of output to input [syn:
       amplification, gain]
    3: (electronics) the act of increasing voltage or power or
       current