dead·pan 
(d
ĕd
p
ăn
′)
n. 1. A blank, expressionless face.
2. A person, especially a performer, who has or assumes a blank expression.
adj. Impassively matter-of-fact, as in style, behavior, or expression: deadpan delivery of the joke.
adv. With a blank, expressionless face.
v. dead·panned, dead·pan·ning, dead·pans
v. tr. To express in an impassive, matter-of-fact way.
v. intr. To express oneself in an impassive, matter-of-fact way.
[DEAD + PAN, the face.]