Q: What is the etymology of “deadpan”? My theory is that it has something to do with musketry, but I haven’t been able to confirm this. Do you know?
A: Your theory about musketry is interesting, but it misses the mark.
“Deadpan” (also spelled “dead pan” and “dead-pan”) actually began life as a theatrical term, according to the Random House Historical Dictionary of American Slang.
The term, which refers to a blank, impassive expression¸ can be a noun, a verb, an adjective, or an adverb.
The first published reference in Random House for the noun is from a 1927 issue of Vanity Fair: “A ‘poker-face’ or ‘dead-pan’ is a lifeless facial expression.”
The first citation for the adverb or adjective is from a 1928 issue of the New York Times: “Dead-Pan – Playing a rôle with expressionless face as, for instance, the work of Buster Keaton.”
The verb first shows up in a 1942 wartime issue of Life magazine: “A Jap press officer dead-pans the news that Singapore is fallen.”
The Oxford English Dictionary has this example from Nathanael West’s 1933 novel Miss Lonelyhearts:
“He practiced a trick used much by moving-picture comedians – the dead pan. No matter how fantastic or excited his speech, he never changed his expression.” (“Dead pan” here is a noun phrase.)
By the way, the second part of the term probably comes from the slang use of “pan” to mean face. The OED’s first citation for this usage is from a 1920 issue of the New York Tribune: “Some drops from it fell on her pan.”
Interestingly, the OED has references going all the way back to Anglo-Saxon days for “pan” used in reference to the head or skull, especially the flat, pan-like, upper part of the skull. Even today, the cranium is sometimes called the “brainpan.”