To plunge means to move or fall suddenly and forcefully downward, often into something. When a diver plunges into a pool, they jump in headfirst with speed and commitment. A roller coaster plunges down a steep track, making riders' stomachs flip. If you drop a stone off a cliff, it plunges toward the ground below.

The word captures that sense of sudden, rapid descent. Temperatures can plunge overnight when a cold front arrives, dropping from pleasant to freezing in hours. Stock prices plunge when investors panic and sell rapidly. A football running back might plunge through the defensive line, driving forward with power.

You can also plunge into activities or situations, meaning you start them boldly without hesitation. A student might plunge into a difficult book, diving right in despite its challenging vocabulary. When you plunge your hand into a bucket of ice water, you're not testing it cautiously: you're committing completely.

The word often suggests courage or recklessness, depending on context. Sometimes plunging ahead works brilliantly; other times, it might have been wiser to wade in carefully. A plunge can also be used as a noun, like taking the plunge when you finally decide to do something you've been nervous about.