verb.to cause to penetrate or enter quickly and forcibly into something

• plunged the dagger
• plunged the nation into economic depression

verb.to cause to enter a state or course of action usually suddenly, unexpectedly, or violently

• plunged off the embankment
• plunges into project after project

verb.to thrust or cast oneself into or as if into water

• the stock's value plunged

noun.an act or instance of plunging: dive; also: swim