fearful (adj.)youdaoicibaDictYouDict[fearful 词源字典]
mid-14c., "causing fear," from fear (n.) + -ful. Meaning "full of fear, timid" (now less common) also is from mid-14c. As a mere emphatic, from 1630s. Related: Fearfully; fearfulness.[fearful etymology, fearful origin, 英语词源]