Rapidly means happening very quickly or at a fast pace. When ice cream melts rapidly on a hot day, it turns from solid to liquid in just minutes. When a fire spreads rapidly through dry grass, it moves so fast that firefighters have to act immediately.

The word emphasizes speed and pace. A rapidly growing plant might shoot up several inches in a week. Technology advances rapidly, meaning new inventions and improvements appear constantly, sometimes making last year's devices feel outdated.

You'll often see this word describing change or movement: a rapidly beating heart, rapidly improving skills, or populations growing rapidly. It suggests something is moving or changing faster than normal or faster than expected. If your math skills improve rapidly after you start practicing every day, you're getting better much faster than you thought you would.