Green’s Dictionary of Slang

any nameless small object, typically some form of gadget.

1914		Our Navy (U.S.) Nov. 12: We were compelled to christen articles beyond our ken with such names as ‘do-hickeys’, ‘gadgets’ and ‘gilguys’ .
1918		‘Bartimeus’ Navy Eternal 116: ‘What I should like to know is, what the deuce is a doo-hickie?’ [...] ‘Well, [...] you know more or less what a gadget’s like?’ ‘Yes.’ ‘And a gilguy?’ ‘Yes.’ ‘Well, a doo-hickie is something like that, only smaller as a rule.’.
1925		(con. WWI) Fraser & Gibbons Soldier and Sailor Words 81: Doo Hicky: An airman’s term for any small, detachable fitting.
1942		J. Mitchell ‘Professor Sea Gull’ in Joe Gould’s Secret (1996) 13: William Shakespeare didn’t sit around pecking on a dirty, damned, ninety-five-dollar doohickey.
1949		R. Chandler Little Sister 163: She held this do’hickey in a black gauntleted glove.
1958		L.F. Cooley Run For Home (1959) 275: Ya hafta know how to take that goddamn doo-hickey apart and clean it.
1965		H. Rhodes Chosen Few (1966) 18: You’ll see a lot of that doohicky before you put in much time here.
1979		Fantastic Four Annual 38: You prob’ly had some kind’a doohickey along that’d bring this here chronosquare ta pick us up.
1987		‘Joe Bob Briggs’ Joe Bob Goes to the Drive-In 149: Cherry Dilday, wearin one of those ribbon scarf doohickeys that you just wrap around three parts of your body and tie behind your neck.
1999		J. Ridley Love Is a Racket 47: I tried the little doohickey that worked the window and got nothing.
2001		(con. 1964–8) J. Ellroy Cold Six Thousand 146: Hes set up his Leica [...] He slapped on the zoom doohickey.
2024		D. Swierczynski California Bear 177: ‘The secret to zip ties is the little locking mechanisms in the little buckle doohickey’.