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'

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 grey wall

[ Syn: redoubtable , unnerving ]