deadpan
1. verb To say something in an emotionless manner, often to humorous effect. "Oh, you'll get lots of peace and quiet here," he deadpanned as shrieking kids ran around him.
2. noun A face that lacks expression or emotion. His deadpan makes it impossible for me to ever know if he's being funny or serious.
3. noun One whose face lacks expression or emotion. He looked like a deadpan, so I had no idea what he was thinking.
4. noun Lacking expression or emotion. His deadpan delivery makes it impossible for me to ever know if he's being funny or serious.