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