deadpan (adj.)

Middle English ded, from Old English dead "having ceased to live," also "torpid, dull;" of water, "still, standing," from Proto-Germanic *daudaz (source also of Old Saxon dod, Danish død, Swedish död, Old Frisian dad, Middle Dutch doot, Dutch dood, Old High German tot, German tot, Old Norse dauðr, Gothic dauþs "dead"), a past-participle adjective based on *dau-, which is perhaps from PIE *dheu- (3) "to die" (see die (v.)).

Meaning "insensible, void of perception" is from early 13c. Of places, "inactive, dull," from 1580s. Of sound, "muffled," 1520s. Used from 16c. as "utter, absolute, quite" (as in dead drunk, 1590s); from 1590s as "quite certain, sure, unerring;" by 1881 as "direct, straight." Dead heat, a race in which more than one competitor reaches the goal at the same time, is from 1796. The dead-nettle (c. 1400) resembles the nettle but does not sting.

Dead on is 1889, from marksmanship. Dead duck "person defeated or soon to be, useless person" is by 1844, originally in U.S. politics. Dead letter is from 1703, used of laws lacking force as well as uncollected mail. Dead soldier "emptied liquor bottle" is from 1913; the image is older (compare dead men "bottles emptied at a banquet," c. 1700). Dead man's hand in poker, "pair of aces and pair of eights," is supposedly what Wild Bill Hickock held when Jack McCall shot him in 1876. Expression not be (seen/found/caught) dead "have nothing to do with" is by 1915.

"broad, shallow vessel of metal used for domestic purposes," Middle English panne, from Old English panne, earlier ponne (Mercian) "pan," from Proto-Germanic *panno "pan" (source also of Old Norse panna, Old Frisian panne, Middle Dutch panne, Dutch pan, Old Low German panna, Old High German phanna, German pfanne), probably an early borrowing (4c. or 5c.) from Vulgar Latin *patna. This is supposed to be from Latin patina "shallow pan, dish, stew-pan," from Greek patane "plate, dish," from PIE *pet-ano-, from root *pete- "to spread."

But both the Latin and Germanic words might be from a substrate language [Boutkan]. Irish panna probably is from English, and Lithuanian panė is from German.

The word has been used of any hollow thing shaped somewhat like a pan; the sense of "head, top of the head" is by c. 1300. It was used of pan-shaped parts of mechanical apparatus from c. 1590; hence flash in the pan (see flash (n.1)), a figurative use from early firearms, where a pan held the priming (and the gunpowder might "flash," but no shot ensue). To go out of the (frying) pan into the fire "escape one evil only to fall into a worse" is in Spenser (1596).