Wordology, Doohickey

The word first appeared in the November 12, 1914 edition of Our Navy magazine, where it states, “We were compelled to christen articles beyond our ken with such names as ‘do-hickeys’, ‘gadgets’ and ‘gilguys’.”
A Sailor Boy’s Log by Robert Brown in 1886, where he also notes one of the first known instances of “gadget”- “Then the names of all the other things on board a ship! I don’t know half of them yet; even the sailors forget at times, and if the exact name of anything they want happens to slip from their memory, they call it a chicken⁓fixing, or a gadjet, or a gill-guy, or a timmey-noggy, or a wim-wom.”
Doohickey soon spread to being used by airman as well, with it noted in Edward Fraser & John Gibbons’ 1925 Soldier & Sailor Words, that “doo hickey” was an airman’s term for small, detachable fittings. Within a couple decades, the word was being used widely throughout America as a placeholder name for anything one could not remember the name of.
Doohickey probably derives from “doodad,” which has uncertain origin, but first popped up in documented form about a decade before “doohickey,” with doodad meaning “a superfluous ornament.” The sailors simply meshed this term with “hickey,” which meant “a device for bending a conduit or a small fitting used in wiring for electric lights, a fixture piped for gas."
Who first used the term “doohickey” has been lost to history. Other names used around the time were doodad, hickey, doojigger, thingamawhatsit, watchamacallit, thingummy, gadget, widget, gilguy, etc.

Incidentally, during the late 1920s or early 1930s, hickey mostly referred to pimples, then other marks on teenager necks, and later began being used by printers to refer to various blemishes in engravings.