The Collaborative International Dictionary of English v.0.48:

eruption \e*rup"tion\, n. [L. eruptio, fr. erumpere, eruptum, to
   break out; e out + rumpere, to break: cf. F. ['e]ruption. See
   Rupture.]
   1. The act of breaking out or bursting forth; as:
      (a) A violent throwing out of flames, lava, etc., as from
          a volcano or a fissure in the earth's crust.
      (b) A sudden and overwhelming hostile movement of armed
          men from one country to another. --Milton.
      (c) A violent commotion.
          [1913 Webster]

                All Paris was quiet . . . to gather fresh
                strength for the next day's eruption. --W.
                                                  Irving.
          [1913 Webster]

   2. That which bursts forth.
      [1913 Webster]

   3. A violent exclamation; ejaculation.
      [1913 Webster]

            He would . . . break out into bitter and passionate
            eruditions.                           --Sir H.
                                                  Wotton.
      [1913 Webster]

   4. (Med.) The breaking out of pimples, or an efflorescence,
      as in measles, scarlatina, etc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

eruption
    n 1: the sudden occurrence of a violent discharge of steam and
         volcanic material [syn: volcanic eruption, eruption]
    2: symptom consisting of a breaking out and becoming visible
    3: (of volcanos) pouring out fumes or lava (or a deposit so
       formed) [syn: eruption, eructation, extravasation]
    4: a sudden violent spontaneous occurrence (usually of some
       undesirable condition); "the outbreak of hostilities" [syn:
       outbreak, eruption, irruption]
    5: a sudden very loud noise [syn: bang, clap, eruption,
       blast, bam]
    6: the emergence of a tooth as it breaks through the gum

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "eruption":
   access, belch, blaze, blaze of temper, blowout, blowup,
   breaking out, burst, cascade, convulsion, cyclone, debouchment,
   diaper rash, discharge, disgorgement, dissiliency, drug rash,
   efflorescence, ejaculation, emission, eructation, explosion,
   expulsion, extravasation, fit, flare, flare-up, gale, gush, gust,
   heat rash, high words, hives, hurricane, irruption, jet,
   nettle rash, outbreak, outburst, outpour, papular rash, paroxysm,
   prickly heat, rapids, rash, rupia, rush, sally, scene, seizure,
   skin eruption, spasm, spate, spew, spout, spouting, spurt, squirt,
   storm, tempest, tornado, torrent, upheaval, urticaria,
   vaccine rash, volcan, whirlwind