formidable formidable /ˌfɔrˈmɪdəbəl/

adjective

1. () Inspiring fear  ( unnerving , doubtable [Archaic] , redoubtable , formidable )
   inspiring fear
    The formidable prospect of major surgery
   the formidable prospect of major surgery
    A tougher and more redoubtable adversary than the heel-clicking, jackbooted fanatic
   a tougher and more redoubtable adversary than the heel-clicking, jackbooted fanatic
    Something unnerving and prisonlike about high grey wall
   something unnerving and prisonlike about high grey wall
   
2. () Extremely impressive in strength or excellence  ( formidable )
   extremely impressive in strength or excellence
    A formidable opponent
   a formidable opponent
    The challenge was formidable
   the challenge was formidable
    Had a formidable array of compositions to his credit
   had a formidable array of compositions to his credit
    The formidable army of brains at the Prime Minister's disposal
   the formidable army of brains at the Prime Minister's disposal