formidable

Adjective

• 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
    

• 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
    

Related words

• Synonyms: 
  redoubtable , unnerving