spook

(noun) someone unpleasantly strange or eccentric. Synonyms: creep, weirdo, weirdie, weirdy.

(noun) a mental representation of some haunting experience. Synonyms: ghost, shade, wraith, specter, spectre. Examples: "He looked like he had seen a ghost." "It aroused specters from his past."

(verb) frighten or scare, and often provoke into a violent action. Example: "The noise spooked the horse."