dreadful (adj.)youdaoicibaDictYouDict[dreadful 词源字典]
early 13c., "full of dread," from dread (n.) + -ful. Meaning "causing dread" is from mid-13c.; weakened sense of "very bad" is from c. 1700. Related: Dreadfully.[dreadful etymology, dreadful origin, 英语词源]