breakthrough; great discovery
Used for a major scientific, academic, or investigative finding; often implies a sudden, important advance.
The researcher made a historic breakthrough.
This great discovery contributed greatly to the advancement of medicine.
突破口 is a 'breakthrough' in a figurative sense, often for solving a problem or breaking a deadlock, while 大発見 focuses on the discovery itself.
Compound of 大 (dai, 'big, great') and 発見 (hakken, 'discovery').