if people, things or situations are formidable, you feel fear and/or respect for them, because they are impressive or powerful, or because they seem very difficult In debate he was a formidable opponent. Somehow the small but formidable woman fought her way through the crowd to reach her son. She has a formidable list of qualifications. The two players together make a formidable combination. The task was a formidable one. They had to overcome formidable obstacles.