Other forms: ugliest, uglier
Ugly means very unpleasant to look at. An ugly building, an ugly jumper. It is a blunt word and applying it to a person's appearance is straightforwardly cruel, which is why it is used far more often about objects.
It has a second sense about situations rather than looks: an ugly mood, things turned ugly, an ugly scene. There it means threatening and about to become violent, and that use is common in news reporting. Note that ugly ends in -ly and is an adjective, like lovely and friendly, so there is no adverb form. And ugly duckling, from the Hans Christian Andersen story, means somebody who turns out beautiful after all.
1adjectiveuglyVery unpleasant to look at.
“It is an ugly building and everybody says so.”
synonyms: unattractive, hideous
2adjectivethreateningThreatening and likely to turn violent.
“The mood outside was getting ugly.”
ugly is a quality of appearance.
Old Norse uggligr meant dreadful or fearful, from ugga, to fear. Ugly was originally about what frightened you rather than what looked wrong, which is why the sense of an ugly mood is closer to the original than the one about appearance.
Old Norse
uggligr — fearful, dreadful, horrible in appearance
Middle English
ugly
English, today
ugly
Built from
Middle English ugly, uggely, uglike, borrowed from Old Norse uggligr (“fearful, dreadful, horrible in appearance”), from uggr (“fear, apprehension, dread”) (possibly related to agg (“strife, hate”)), equivalent to ug + -ly. Cognate with Scots ugly, uglie, Icelandic ugglegur. Meaning softened to "very unpleasant to look at" around the late 14th century, and sense of "morally offensive" attested from around 1300. For the meaning development compare грозен (< grozьnъ), стра́шный (< strašьnъ < straxъ); foedus (< bʰeyh₂-).
Etymology from Wiktionary, CC BY-SA