Despite repeated questioning, he remained closed-mouthed about the details of the case.

closed-mouthed 是由形容词 closed（关闭的）和名词 mouth（嘴巴）加上后缀 -ed 组成的复合形容词。字面意思是"嘴巴紧闭的"，引申为"不愿透露信息的、守口如瓶的"。 这个复合词形象地描述了一个人拒绝开口说话的状态，就像嘴巴被关闭了一样。