①keep a straight face绷着脸；努力不笑出来

②straight face不露表情的脸

③straight-faced面无表情的

实例：

1.What went through Tom's mind I can't imagine, but he did manage to keep a straight face.

不知道Tom想到了啥，但他确实忍住没笑。

2.I can never play jokes on people because I can't keep a straight face.

我从来都不能和别人开玩笑，因为我很难绷着不笑出来。

出处：头条号 @坚小持微课