unsmiling
adj. 严肃的；不笑的
例句
He was unsmiling and silent.
他十分严肃，一言不发。
《柯林斯英汉双解大词典》
His eyes were hard and unsmiling.
他目光严厉冷峻。
《牛津词典》
We often keep a straight face or use an unsmiling expression when we're making a joke.
当我们开玩笑的时候，我们经常绷着脸或使用不笑的表情。
