Green’s Dictionary of Slang

any nameless small object, typically some form of gadget.

1931		L. Pound ‘American Indefinite Names’ in AS VI:4 258: Indefinite names... Thingum [...] thingem-bob [...] doosenwhacker, doowhacker, doowhackie, doowhopper [...] dudenwhacker.
1942		Berrey & Van den Bark Amer. Thes. Sl. 75.4: Contrivance; indefinite object; ‘gadget.’ [...] dowhacker, dowhackie, dowhacky, dowhackus, dowhopper.
1969		in DARE II 139/2: Doowitchet.
1991		in DARE II 139/2: doowhacker n Also doosenwhacker, doowhopper, doowitchet.
2000		M. White Atlas of the 20th Century 🌐 One day I was looking up the spelling of Czechoslovakia (Checkoslovokia?), and I discovered that the people who lived there actually called it ‘Ceskoslovensko’, with a little doowhacker over the C.