Oxymoron is a figure of speech in which contradictory or incongruous words are combined. In the given sentence, an example of oxymoron is <em>alone together. </em>When someone is alone, they are on their own, with no one else present. However, the word <em>together</em> implies that two or more people are present. This is why it's unusual to see these words combined. Their meanings are contradictory, which makes this an oxymoron.
A higher-level text in the Townsend Press vocabulary series, Advancing Vocabulary Skills<span>, 4/e is suitable for intermediate and advanced developmental courses.</span>