thingumabob; thingummybob noun used as a replacement for any noun that the user cannot or does not wish to specify UK,1832
[W]hat the Sam Hill is this thingumabob supposed to do? — Eric Kraft, Herb‘n’Lorna, p. 188, 1989
“But I tell you, when I turned my head and saw that fancy ultra-business thingummybob . . .” “Ultrasound,” corrects Clara, through a mouthful of rice. — Zadie Smith, WhiteTeeth, p. 57, 2000