Definitions of plunge:

• noun:   a steep and rapid fall
• noun:   a brief swim in water
• verb:   begin with vigor

  Example: "She plunged into a dangerous adventure"

• verb:   cause to be immersed

  Example: "The professor plunged his students into the study of the Italian text"

• verb:   dash violently or with great speed or impetuosity

  Example: "She plunged at it eagerly"

• verb:   fall abruptly

  Example: "It plunged to the bottom of the well"

• verb:   thrust or throw into
• verb:   drop steeply

  Example: "The stock market plunged"

• verb:   engross (oneself) fully
• verb:   immerse briefly into a liquid so as to wet, coat, or saturate