The phrase "rattling on" is often used to describe someone who is talking excessively or pointlessly. Antonyms for this expression could include being concise, brief, or succinct. Other words that might relate to this concept include being direct, to-the-point, or focused. By contrast, rambling, meandering, or wandering might be considered antonyms for the idea of being concise. Other words that could convey the opposite of the phrase "rattling on" might include being silent, quiet, or reserved. These are all ways to describe someone who is not prone to excessive talk or who is able to communicate effectively without going on and on.