Pretty is a funny word. By funny I don’t mean ‘haha’ funny but ‘weird’ funny. Come to think of it, funny is a funny word too and thus it may appear in a future WOTD post. But pretty is a funny word because it has more than one rhetorical meaning.
It’s primarily defined as an adjective that describes something aesthetically pleasing in appearance.For example: Those flowers are pretty. See how the word pretty as an adjective clearly modifies the plural noun flowers.
However, today’s word has a secondary rhetorical function as an adverb, which has much the same meaning as the words: very, really, quite and other similar words.
(This is where the funny part comes in.)
Since the word pretty can be used as an adverbial modifier, this means that the phrasal adjective “pretty ugly” makes perfect rhetorical sense and it is not at all an oxymoron. Even though it definitely looks like one.