Green’s Dictionary of Slang

1. (also jewels) the male genitalia; cites 1970 spec. the penis.

1916		H.N. Cary Sl. of Venery.
c.1935		‘Mae West in “The Hip Flipper”’ [comic strip] in B. Adelman Tijuana Bibles (1997) 97: His Nibs is ready to surrender the family jewels to our Lotta, especially that three piece set he’s got up Lotta’s flue right now.
1958		(con. 1950) E. Frankel Band of Brothers 2: I got booted in the family jewels playin’ football.
1964		R. Helmer Stag Party 82: Pickle me bloody agates, would you believe it? The bullet has caught the old boy clean in the family jewels.
1970		‘Troy Conway’ Cunning Linguist (1973) 109: Her body plastered itself against me and so help me, my loins stirred and my family jewels stood on end.
1970		‘Troy Conway’ Cunning Linguist (1973) 145: I alternately plunged and stabbed, using each lush mouth as a scabbard to sheathe the family jewels.
1985		(con. 1968) D.A. Dye Citadel (1989) 330: Not a scratch on the family jewels or the scepter that goes with them.
1992		(con. 1920–57) Randolph & Legman Ozark Folksongs and Folklore II 787: Other common names for the male organ are [...] family organ [or family jewels].
1993		S. King Dolores Claiborne 111: He looked like I’d hoicked my knee right up into his family jewels.
1997		Roger’s Profanisaurus in Viz 87 Dec. n.p.: family jewels euph. The knackers; male genitalia.
1999		R.G. Barrett Wind & Monkey (2013) [ebook] The family jewels weren’t going to be much use to him for a long, long time.
2007		N. ‘Razor’ Smith Raiders 307: He also suffered third-degree burns on his family jewels.
2012		D. O’Donnell Locked Ward (2013) 276: She struggled and fought [...] and tried to knee me in the family jewels.
2016		N. Cummins Adventures of the Honey Badger [ebook] VITAL AUSSIE VERNACULAR Squeezed Testicles [...] 4. Grabbing the family jewels.
2023		R. Milward Man-Eating Typewriter 202: Nix jewels. nanti testicles! Vomitus leapt up my gargler.

2. wealth, ready money.

1972

(con. 1950s) D. Goines Whoreson 92: Fifty-two dollars was the family jewels.

3. in fig. use, something very valuable.

1977

(con. 1960s) D. Goines Black Gangster (1991) 74: It might just cost us our family jewels if this stud ain’t cool.