Green’s Dictionary of Slang

1. the police.

1989		(con. 1982–6) T. Williams Cocaine Kids (1990) 136: five-o the police.
1989		Ice-T ‘You Played Yourself’ 🎵 When you go to sleep you count five-ohs.
1991		D. Gaines Teenage Wasteland 79: By 9:20, ‘Hawaii 5-0’ will arrive and with them threat of parking tickets, beer tickets, and formal charges.
1993		A. Rodriguez Spidertown (1994) 51: One kid got hit, but it wasn’t bad, didn’t even have t’call the 5-0.
2000		P. Beatty Tuff 70: When five-o blow up the spot, they treat the white boys like day campers.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 70/1: five-O n. a police officer, esp. a detective or an undercover officer.
2004		N. Kelley ‘The Code’ in Brooklyn Noir 172: Wounds received from rival niggaz and Five-Os.
2007		D.S. Mitchell Killer Tune (2008) 47: Call Five-O [...] Call the fucking police!
2010		Codella and Bennett Alphaville (2011) 4: FiveO, Five-O. Yo, Rambo on the block.
2011		G. Knight Hood Rat 116: Don’t come out the back [...] Five-oh are here.
2011		J. Cornish Attack the Block [film script] 32: The POLICE VAN BREAKS HARD, doors are thrown open, TWO OFFICERS LEAP out [...] PESTFuck the five-o!
2016		V. McDermid Out of Bounds (2017) 4: Some bastard had phoned them in and the five-oh were coming to get them.
2017		S.M. Jones August Snow [ebook] ‘Muhfuckin’ five-oh, man’.

2. attrib. use of sense 1.

2002

D.H. Sterry Chicken (2003) 196: In my rearview mirror is a cop. He’s giving me the hardcore five-oh eyeball.

3. a 50-litre Ford Mustang (used as a police vehicle in some areas).

1995		M. Mueller Ford Mustang 69: Of course, there were some who were sorry to see the Fox-chassis ‘Five-Oh’ Mustang go.
2003		R. Wood Lightning Crashes 70: A nineteen eighty-eight GT Mustang [...] was as far removed from the old Five-Oh as the plankton was from the whale.

4. (US drugs) a $50-rock of cocaine.

1985

T.R. Houser Central Sl.

5. (US prison) a prison officer.

2000

Other Side of the Wall: Prisoner’s Dict. July 🌐 5-0: Correctional officer. (FL / NC).