Formidable means impressively powerful, skillful, or difficult to deal with. A formidable opponent in chess makes you think carefully about every move because they're so good at the game. A formidable challenge, like climbing a steep mountain or mastering a difficult piano piece, demands serious effort and respect.

The word carries a sense of strength that inspires both admiration and caution. A formidable debater argues so effectively that even if you disagree, you recognize their skill. A formidable fortress in medieval times had walls so thick and defenses so strong that armies hesitated to attack.

Something formidable doesn't have to be threatening, though. A formidable scientist might make groundbreaking discoveries through brilliant thinking. A formidable reputation means people know you're exceptionally capable at something. When teachers describe a project as formidable, they mean it will test your abilities, but they're not saying it's impossible, just that it deserves your full attention and best effort.

The key is that formidable things command respect through their impressive power or complexity. They combine difficulty or strength with a quality that makes you admire them. When you face something formidable, you know you'll need to bring your best skills and determination to succeed.