Green’s Dictionary of Slang

1. (orig. US black, also eight-pack) a tight, flat stomach; also attrib. [the ripples resemble beer cans].

1998		Guardian Guide 25–31 Jul. 23 n.p.: Sure, Pitt, Affleck and Damon all have the sixpacks to carry off Boogie Nights’ Eddie Adams.
1998		R.G. Barrett Goodoo Goodoo 22: A super-fit-lloking brunette with a sixpack stomach.
1999		Guardian Rev. 25 June 5: Marky and his homies [...] displaying their oiled-up six-packs.
2000		F.X. Toole Rope Burns 108: ‘Look at my eight-pack,’ he said, lifting his T-shirt so Con could see his abdominals.
2000		Guardian 14 Jan. 32: You know, diet, training, fitness, six pack, buns of steel.
2004		T. Winton Turning (2005) 155: He had real pecs and a six-pack.
2008		A. Wheatle Dirty South 59: A tonk looking brother was approaching us [...] This guy had He-Man muscles on his neck and probably owned an eight-pack.
2015		J. Stahl OG Dad 261: An actual toddler trainer. Working those little baby abs so they’ll be mini six packs by summer.

2. (Ulster) a paramilitary punishment involving shots to the knees, ankles and hands.

1994		P. O’Gorman Queuing for a Living n.p.: ‘A 6-pack?’ ‘That there’s the hands, the knees, the ankles’ [BS].
2005		Guardian 9 Mar. 1/4: They were to be punished with a [...] ‘six-pack’ where victims are shot in the ankles, knees and elbows.

3. (US police) an array of photos to be shown to witnesses comprising a photo of the suspect andof five others.

2002

R. Sullivan LAbyrinth 41: They needed a recent picture of Gaines, the Wilshire detective said, to use in a six-pack photo lineup.