Definition of "whatchamacallit"

The Thingamajig and the Wachamacallit.

1921, Johnny Gruelle, Orphant Annie Story Book, Volume 7, page 69

You’re—you must be the whatchamacallit, huh? The peer.

1969, J[ames] P[inckney] Miller, stage adaptation by F. Andrew Leslie, The People Next Door, New York, N.Y.: Dramatists Play Service, act II, page 42

JESSICA: How many times do I have to say it? We were not stealing, Officer. We were just— / MONAHAN: I know. Performing some kind of whatchamacallit deed. Anyhow, they go to the clink, that's what happens to people who filch city property.

1972, Carolyn Lane, Child of Air: A One Act Play, Denver, Colo.: Pioneer Drama Service, page 13

I'm a boy, so when I'm sick, they can call in poohaghooma, Indian doctor. But not Tom Mitchell! No, sir! [We] won't have Tom Mitchell to doctor me! 'Cause whatchamacallit, he always used to doctor me …

1996, Corbett Mack, as told by Michael Hittman, “Boyhood (1892–1905)”, in Corbett Mack: The Life of a Northern Paiute (Studies in the Anthropology of North American Indians), Lincoln, Neb., London: University of Nebraska Press, page 60

"Think we ought to check this whatchamacallit?" / "No, that doodad over there seems to be the problem."

1998, David Alan Black, “There’s No Place Like Rome: The Parts of Speech and Their Function”, in It’s still Greek to Me: An Easy-to-understand Guide to Intermediate Greek, Grand Rapids, Mich.: Baker Books, page 19

As you've said, the safety of the American people is our first priority. We have orders that if these EMP whatchamacallits can't be secured then they must be destroyed.

2014 October, Don Pendleton, chapter 15, in Domination Bid (Don Pendleton’s Stony Man: America’s Ultra-covert Intelligence Agency; Gold Eagle Book), Don Mills, Ont.: Worldwide Library, page 180