Redoubtable means honorable, maybe even intimidatingly so. If your grandmother worked tirelessly to raise four kids on her own and start her own taxi cab business and to this day, keeps all of her cabbies in line, she is without a doubt redoubtable.
The adjective redoubtable traces back to the French word redute, meaning “to dread,” a combination of the prefix re-, which adds emphasis, and duter, which mean “to doubt.” But it isn't the redoubtable person that you doubt — it's yourself or your ability to compete against or be compared to him or her. That's where the dread comes in. But you can learn a lot from and be inspired by redoubtable people, if you can just get over being afraid of them.