deadpan >> /ˈdɛdˌpæn/
Definition: [adverb] In a deadpan manner.
Example: “That's all right then,” Claire said, deadpan
Definition: [verb] Say something amusing while affecting a serious manner.
Example: “I'm an undercover dentist,” he deadpanned
Definition: [adjective] Deliberately impassive or expressionless.
Example: answers his phone in a deadpan tone