unnerving

(verb) disturb the composure of. Synonyms: faze, unnerve, enervate, unsettle.

(adj) 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 grey wall."