- formidable - 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"
Antonym: unimpressive (indirect, via impressive)
- formidable, redoubtable, unnerving - 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"
Antonym: unalarming (indirect, via alarming)