Green’s Dictionary of Slang

an unspecified, un-named person or object.

1920		Bulletin (Sydney) 11 Mar. 20/2: [He] strolled happily away to see if old Bill Whosit still kept the pub.
1975		J. Roe Same Old Grind 111: ‘[T]he doodad he’s got around his gizmo falls off and [...] in the meantime, these rubber boobies come flying up out of the hoosit around his chest’.