Green’s Dictionary of Slang

1. anything or anyone for which one cannot remember the name.

1900		Sydney Sportsman (Surry Hills, NSW) 31 Oct. 1/3: He still remains elegible for a doodah Park stakes.
1904		Sydney Sportsman (Surry Hills, NSW) 13 July 4/3: The second heat give the ‘doodahs’ a chance to get together and earn a bob or two.
1921		D.L. Sayers Unpleasantness at the Bellona Club (1977) 38: D’you mind stickin’ all those dark-slides into one pocket and a few odd lenses and doodahs into the other.
1941		G. Kersh They Die with Their Boots Clean 91: I’ve got the numbering kit here, ink-pad, stamps and doo-dahs.
1958		J. Sandford Whelks and the Chromium (1968) 125: Ken, now you go on the doodah!
1977		(con. 1969) M. Herr Dispatches 20: Maintaining the equilibrium of the Dingdong by containing the ever encroaching Doodah.
1986		L. Heinemann Paco’s Story (1987) 16: Parson Doo-dah’s Meeting House Revival.
2012		R. Milward Kimberly’s Capital Punishment (2023) 423: I carry on with doodah’s blood extraction.
2013		K. Sampson Killing Pool 68: Pen? Are you on the doodah?

2. the genitals.

1995		H. Kureishi Black Album 195: ‘But I don't put an essay on [...] the odours of their body and everything like that — people sniffing one another’s, you know, doo-dahs.’ ‘Didn't God give us our doo-dahs?’ ‘I wouldn't put them into print!’.
2005		Observer Mag. 27 Nov. 10: Believe me you don’t want to be spilling piping hot coffee on your doo-dahs.

3. see doodad n. (3)