tight-lipped
tight-lipped
/ˌtaɪt ˈlɪpt/
1 not willing to talk about something
Despite the rumours, government officials remained tight-lipped today.
2 keeping your lips pressed together, especially because you are angry about something
He marched out of the room tight-lipped and white-faced.
a tight-lipped reply
e.g.
Anyone involved has probably been tight-lipped about the incident, especially since they're trying to get the gold themselves. 事件にかかわった役人たちが金塊欲しさに隠していたんだろう (/yupeco/『ゴールデンカムイ』2話)