1. extremely impressive in strength or excellence;
"a formidable opponent""the challenge was formidable""had a formidable array of compositions to his credit""the formidable army of brains at the Prime Minister's disposal"
2. inspiring fear;
"the formidable prospect of major surgery""a tougher and more redoubtable adversary than the heel-clicking, jackbooted fanatic"- G.H.Johnston"something unnerving and prisonlike about high gray wall"