Button 是纽扣，lip 是嘴唇，Button one's lip 字面意思是“嘴唇装上纽扣”，真实含义是“闭嘴；闭口不谈，缄默，保持缄默”。

【例句】
Hey, button your lip! We don't need to hear any more out of you today!
嗨，闭上你的嘴巴！我们今天不想听见你说更多的话！

He didn't want to get into a fight, so he decided to button his lip.
他不愿意卷入一场争执，于是决定保持缄默。