We wondered in the last class if oxymorons could be two or three words widely separated in the sentence. While they can be more than two words-- seems four is the longest--they generally consist of words right next to each other, for instance, "cruel kindness," "adult children," and" active retirement".
Here's a list, although some of the examples might be tongue in cheek (meant to be amusing) because. for the life of me, I don't see why "adult male" is considered an oxymoron. If you can explain that one, please do.