unnerving
1. [ adjective ] inspiring fear
Synonyms: formidable redoubtable
Examples:

"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 gray wall"

Related terms: alarming
Similar spelling:   unrevealing
  unnerve
  unnerved
  unrefined
  unreproved