frightful (adj.) Look up frightful at Dictionary.com
mid-13c., "timid;" c.1600 "alarming;" from fright + -ful. In common with most -ful adjectives, it once had both an active and passive sense. Meaning "dreadful, horrible, shocking" (often hyperbolic) is attested from c.1700; Johnson noted it as "a cant word among women for anything unpleasing." Related: Frightfully.