Sing along with this synonym and antonym rap song to learn when and how to use synonyms and antonyms. Synonyms say the same thing again and again. Antonyms don’t mean the same thing - they mean the opposite. You can use synonyms when you want to describe something but don’t want to use the same word over and over again, lest you get boring and repetitive. Use an antonym when you want to describe the opposite of something, like day and night.