Green’s Dictionary of Slang

1. (orig. US, also gismo) any (small) thing for which one has temporarily forgotten the correct name, a gadget.

1942		Honolulu Star Bull. (HI) 28 Nov. 6/1: When a sailor can’t recall the name of a thing, he invariably refers to it as a ‘gismo’.
1945		N.Y. World-Telegram 21 Feb. n.p.: Gizmo [...] something that can be used for anything.
1953		L. Uris Battle Cry (1964) 436: We’ve got to go gizmo hunting.
1962		E. Stephens Blow Negative! 139: It’s a funny kind of Cuban gismo you can‘t see through.
1969		‘Iceberg Slim’ Pimp 67: Some steamed up joker in the adjoining room had his gizmo focussed on the carnival.
1979		Fantastic Four Annual 7: Turn them blasted gizmos off!
1979		E. Torres After Hours 4: The MCC is a fancy building with a lot of electronic gadgets and gismos.
1986		L. Heinemann Paco’s Story (1987) 23: The cap would flip open this bullshit company compass he had [...] thinking to himself, What is this goddam gizmo?
1998		Hip-Hop Connection Dec. 5: You could win Tiger’s latest little gizmo, a bottle opener come drinking game.
1999		J. Baker Walking With Ghosts (2000) 2: A telephone/fax/intercom gismo.
2001		N. Barlay Hooky Gear 235: Hes checkin the meter I never fed an course next thing his brains workin overtime tryin to punch the plate number in his gismo.
2006		D. Mitchell Black Swan Green 148: I know your fork-lift gizmo was an unexpected expense.
2021		J. Ellroy Widespread Panic 179: Donkey Don worked the sound gizmo.

2. (US drugs) the paraphernalia used for injecting narcotics.

1960		P. Rabe My Lovely Executioner (2006) 132: You see some horrible thing, some gizmo apparition that’s called an addict.
1987		Eble Campus Sl. Spring 9: works – syringe for injecting drugs. Also things, gadgets, gizmo.
1993		E. Richards Cocaine True 64: Syringes, toys, gizmos, guns, works, call ’em what you want.

3. (US, also gismo) the vulva or vagina.

1942–48		in So. Folklore Quarterly XIII (1949) 205: Gismos [...] (sometimes used particularly in reference to parts of the female anatomy – definitely old navy) [HDAS].
1962		P. Crump Burn, Killer, Burn! 242: Cool yourself into rigor mortis for not copping righteous on de gismo when you had it on de slaughtering floor.

4. (US) the penis.

1985

oral testimony in Lighter HDAS I.

5. (US) a foolish man.

1949

R. Chandler Little Sister 164: Then I meet this gizmo with her door-key in his hand.