No matter how we asked, she stayed tight-lipped about what happened last night.

tight-lipped 是由形容词 tight（紧的）和名词 lip（嘴唇）加上后缀 -ed 组成的复合形容词。字面意思是"嘴唇紧闭的"，引申为"守口如瓶的"，形容一个人拒绝透露信息或保持沉默的状态。