deadpan

adj. expressionless, without emotion

Deadpan is a form of comedic delivery in which humour is presented without exhibiting a change in emotion or facial expression. Deadpan is a type of dry humour.
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Adjective
1. deliberately impassive in manner; "deadpan humor"; "his face remained expressionless as the verdict was read"
(synonym) expressionless, impassive, poker-faced, unexpressive
(similar) uncommunicative, incommunicative
Adverb
1. without betraying any feeling; "she told the joke deadpan"

with an expressionless or emotionless face He had a deadpan expression when he told us the story.

Synonyms and related words:
blank, cold-bloodedly, coldheartedly, coldly, dispassionately, empty, expressionless, fishy, glassy, heartlessly, impassive, in cold blood, inexpressive, poker-faced, spiritlessly, unemotionally, unexpressive, unfeelingly, unpassionately, vacant, with dry eyes, wooden,