Source : Webster's Revised Unabridged Dictionary (1913)

Plunge \Plunge\, n.
   1. The act of thrusting into or submerging; a dive, leap,
      rush, or pitch into, or as into, water; as, to take the
      water with a plunge.

   2. Hence, a desperate hazard or act; a state of being
      submerged or overwhelmed with difficulties. [R.]

            She was brought to that plunge, to conceal her
            husband's murder or accuse her son.   --Sir P.
                                                  Sidney.

            And with thou not reach out a friendly arm, To raise
            me from amidst this plunge of sorrows? --Addison.

   3. The act of pitching or throwing one's self headlong or
      violently forward, like an unruly horse.

   4. Heavy and reckless betting in horse racing; hazardous
      speculation. [Cant]

   {Plunge bath}, an immersion by plunging; also, a large bath
      in which the bather can wholly immerse himself.

   {Plunge}, or {plunging}, {battery} (Elec.), a voltaic battery
      so arranged that the plates can be plunged into, or
      withdrawn from, the exciting liquid at pleasure.