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

Moby Thesaurus II by Grady Ward, 1.0:

161 Moby Thesaurus words for "amplification":
   access, accession, accomplishment, accretion, accrual, accruement,
   accumulation, addition, adjunct, advance, advancement,
   aggrandizement, aggravation, ampliation, annoyance, appreciation,
   ascent, augmentation, ballooning, ballyhoo, big talk,
   bilingual text, bloating, blossoming, blowing up, boom, boost,
   broadening, buildup, burlesque, caricature, clavis,
   contentiousness, crescendo, crib, decipherment, decoding,
   deepening, deliberate aggravation, deployment, deterioration,
   development, developmental change, dilatation, dilation,
   dispersion, edema, elaboration, elevation, embittering,
   embitterment, enhancement, enlargement, evolution,
   evolutionary change, evolvement, evolving, exacerbation,
   exaggerating, exaggeration, exasperation, excess, exorbitance,
   expansion, expatiation, explication, extension, extravagance,
   extreme, faithful translation, fanning out, flare, flood,
   flowering, free translation, furtherance, gain, gloss, glossary,
   gradual change, grandiloquence, greatening, growth, gush,
   heightening, hike, hiking, huckstering, hyperbole, hyperbolism,
   increase, increment, inflation, inordinacy, intensification,
   interlinear, interlinear translation, irritation, jump, key, leap,
   loose translation, magnification, maturation, metaphrase, mounting,
   multiplication, natural development, natural growth,
   nonviolent change, overemphasis, overestimation, overkill,
   overstatement, paraphrase, pony, prodigality, productiveness,
   profuseness, progress, progression, proliferation, provocation,
   puffery, puffing up, raise, raising, restatement, rewording,
   ripening, rise, sensationalism, sharpening, snowballing, souring,
   splay, spread, spreading, stretching, superlative, surge, swelling,
   tall talk, touting, transcription, translation, transliteration,
   travesty, trot, tumescence, unfolding, up, upping, upsurge,
   upswing, uptrend, upturn, waxing, widening, working-out,
   worsening