UNNERVING
formidable, redoubtable, unnerving
(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”
Source: WordNet® 3.1
Verb
unnerving
present participle of unnerve
Source: Wiktionary
UNNERVE
Un*nerve", v. t. Etym: [1st pref. un- + nerve.]
Definition: To deprive of nerve, force, or strength; to weaken; to
enfeeble; as, to unnerve the arm.
Unequal match'd, . . . The unnerved father falls. Shak.
Source: Webster’s Unabridged Dictionary 1913 Edition