A formidable opponent is one that's very strong or difficult to beat.
You often hear "formidable" used to describe people, teams, or animals that are impressive and hard to defeat. Imagine watching a sports game - if your team is playing against a formidable opponent, it means they're really tough to beat. You might also use the word when talking about a challenge you're facing in life - if something seems formidable, it's daunting or intimidating, but not necessarily impossible to overcome. For example, "The mountain hike was going to be a formidable task" would mean that climbing the mountain is very difficult and requires a lot of effort.
Causing fear, dread, awe, or discouragement as a result of size, strength, or some other impressive feature; commanding respect; causing wonder or astonishment.
