The Collaborative International Dictionary of English v.0.48:

Amplify \Am"pli*fy\, v. i.
   1. To become larger. [Obs.]
      [1913 Webster]

            Strait was the way at first, withouten light,
            But further in did further amplify.   --Fairfax.
      [1913 Webster]

   2. To speak largely or copiously; to be diffuse in argument
      or description; to dilate; to expatiate; -- often with on
      or upon. --Watts.
      [1913 Webster]

            He must often enlarge and amplify upon the subject
            he handles.                           --South.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Amplify \Am"pli*fy\, v. t. [imp. & p. p. Amplified; p. pr. &
   vb. n. Amplifying.] [F. amplifier, L. amplificare. See
   Ample, -fy.]
   1. To render larger, more extended, or more intense, and the
      like; -- used especially of telescopes, microscopes, etc.
      [1913 Webster]

   2. (Rhet.) To enlarge by addition or discussion; to treat
      copiously by adding particulars, illustrations, etc.; to
      expand; to make much of.
      [1913 Webster]

            Troilus and Cressida was written by a Lombard
            author, but much amplified by our English
            translator.                           --Dryden.
      [1913 Webster]

WordNet (r) 3.0 (2006):

amplify
    v 1: increase in size, volume or significance; "Her terror was
         magnified in her mind" [syn: magnify, amplify]
    2: to enlarge beyond bounds or the truth; "tended to romanticize
       and exaggerate this `gracious Old South' imagery" [syn:
       overstate, exaggerate, overdraw, hyperbolize,
       hyperbolise, magnify, amplify] [ant: downplay,
       minimise, minimize, understate]
    3: exaggerate or make bigger; "The charges were inflated" [syn:
       inflate, blow up, expand, amplify]
    4: increase the volume of; "amplify sound"

Moby Thesaurus II by Grady Ward, 1.0:

130 Moby Thesaurus words for "amplify":
   add to, agent provocateur, aggrandize, aggravate, annoy, augment,
   ballyhoo, bloat, blow up, boost, broaden, build, build up, bulk,
   bulk out, burlesque, caricature, carry too far, charge, complete,
   crescendo, deepen, descant, detail, deteriorate, develop, dilate,
   distend, draw the longbow, elaborate, electrify, embellish,
   embitter, embroider, energize, enhance, enlarge, enlarge upon,
   enter into detail, evolve, exacerbate, exaggerate, exalt,
   exasperate, expand, expatiate, explicate, extend, fatten, fill out,
   galvanize, generate, go into, go to extremes, heat up, heighten,
   hike, hike up, hot up, huff, hyperbolize, increase, inflate,
   intensify, irritate, jack up, jump up, labor, lay it on, lengthen,
   loop in, magnify, make acute, make much of, make worse, maximize,
   overcharge, overdo, overdraw, overestimate, overpraise, overreach,
   overreact, oversell, overspeak, overstate, overstress, parlay,
   particularize, pile it on, plug in, provoke, puff, puff up, pump,
   pump up, put up, pyramid, raise, rarefy, rehearse in extenso,
   relate at large, sharpen, shock, short, short-circuit, sour,
   spell out, step down, step up, stiffen, stretch, stretch the truth,
   sufflate, supplement, swell, switch off, switch on, talk big,
   talk in superlatives, thicken, tout, travesty, turn off, turn on,
   unfold, up, widen, work out, worsen