He has mastered a 'formidable' amount of material.
The mountains were a 'formidable' barrier.
a 'formidable' enemy/opponent/weapon
(..) There's no need to be formal or cute about it. As a matter of fact, I rather feel Iike expressing myself now. And I could certainly use a release. - Bonsoir. Vous 'tiez formidable. - Merci. You certainly made friends and influenced people. They're empathicalists. You talk a lot about empathy. (..)1957 Funny Face