Synonyms:
formidable, redoubtable, unnerving
Meaning: 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"
Usage examples
For he himself had vainly sought to put aside the depressing and unnerving conviction that in steadiness, stamina and self-confidence, Rodney Grant was his superior; something he had determined never to breathe to any one else, but which the keen judgment of the team captain had found out.