daunting       
adjective uk/ˈdɔːn.tɪŋ/ us/ˈdɑːn.t̬ɪŋ/
 令人发怵的;使人气馁的
making you feel slightly frightened or worried about your ability to achieve something
  The country was faced with the daunting prospect of overcoming four decades of division. 国家仍然面临着弥合40年的分裂这一难题。 
 Synonym: intimidating