Groundbreaking describes something so new and important that it changes the way people think or do things. When scientists make a groundbreaking discovery, they've learned something no one knew before, something that opens up entirely new possibilities. When an inventor creates a groundbreaking device, it solves problems in ways nobody had imagined.

A groundbreaking idea or achievement marks the beginning of progress in a whole field.

Marie Curie's research on radioactivity was groundbreaking: it led to new medical treatments and to our understanding of atoms. The Wright brothers' first airplane flight was groundbreaking because it proved humans could fly, launching the entire aviation industry. When your class does a groundbreaking experiment, you might be the first students in your school to try that particular method or explore that question.

Not every good idea is groundbreaking. A small improvement to an existing design is helpful but not groundbreaking. Groundbreaking work fundamentally shifts what's possible, like the difference between making a faster horse cart and inventing the automobile. When something is truly groundbreaking, the world afterward looks different than it did before.