The phrase "rattle on" is often used to describe someone who talks excessively, without any intention of stopping. Its antonyms might include "keep quiet," "be still," "shut up," or "remain silent." These words suggest a calm and controlled demeanor, where one chooses not to speak unnecessarily. As a contrast, using "rattle on" indicates an unbridled expression of words, and therefore the opposite would be measured, thoughtful communication. In many cases, a moderate, more measured approach to speech is more effective than an overly vocal one, leading to more productive and meaningful conversations.