uglyyoudaoicibaDictYouDict[ugly 词源字典]
ugly: [13] Ugly originally meant ‘horrible, frightening’; ‘offensive to the sight’ is a secondary development, first recorded in the 14th century. The word was borrowed from Old Norse uggligr, a derivative of the verb ugga ‘fear’. In the early 1930s it was applied, in the altered spelling ugli, to a new sort of citrus fruit, a hybrid of the grapefruit and the tangerine; the reference is to the fruit’s unprepossessing knobbly skin.
[ugly etymology, ugly origin, 英语词源]
ugly (adj.)youdaoicibaDictYouDict
mid-13c., uglike "frightful or horrible in appearance," from a Scandinavian source, such as Old Norse uggligr "dreadful, fearful," from uggr "fear, apprehension, dread" (perhaps related to agg "strife, hate") + -ligr "-like" (see -ly (1)). Meaning softened to "very unpleasant to look at" late 14c. Extended sense of "morally offensive" is attested from c. 1300; that of "ill-tempered" is from 1680s.

Among words for this concept, ugly is unusual in being formed from a root for "fear, dread." More common is a compound meaning "ill-shaped" (such as Greek dyseides, Latin deformis, Irish dochrud, Sanskrit ku-rupa). Another Germanic group has a root sense of "hate, sorrow" (see loath). Ugly duckling (1877) is from the story by Hans Christian Andersen, first translated from Danish to English 1846. Ugly American "U.S. citizen who behaves offensively abroad" is first recorded 1958 as a book title.