Supernatural means "above or beyond what is natural," "miraculous," "abnormal," "not explainable by natural laws," "attributed to the exercise of divine power": "Ancient Greeks and Romans believed in supernatural beings whom they called gods." "The existence of this enormous crater must be traced to supernatural forces." "The guided missile seemed to accelerate at supernatural speed." Unnatural means "contrived," "artificial," "inhuman," "violating natural feelings," "inconsistent with prevailing customs": "This child's treatment of his parents is unnatural." "It is unnatural for a physician to be a sadist." That which is supernatural is unnatural, but much that is unnatural is not supernatural. Related but relatively uncommon words are supranatural, a synonym of supernatural, and preternatural, meaning "exceptional," "unusual," and "abnormal."
Dictionary of problem words and expressions. Harry Shaw. 1975.