When someone is tight-lipped, his or her lips remain firmly closed, especially so as not to show any emotion or to keep information about something to him or herself.
Sometimes, we use it to describe an angry expression.
Let’s see some examples :
– We could all see there was a serious problem, but he remained tight-lipped about it.
– She was tight-lipped our plans for the Christmas holiday.
– the players were tight-lipped about their strategy for the next match.