Green’s Dictionary of Slang

O n.

[abbr.]

1. (US drugs, also oh) an ounce of a narcotic.

[US]D. Maurer ‘Argot of the Und. Narcotic Addict’ Pt 1 in AS XI:2 124/2: o. 1. Among addicts who use the needle it refers to an ‘ounce’ or piece of dope, especially of morphine.
[US]J.E. Schmidt Narcotics Lingo and Lore.
[US]J. Wambaugh Golden Orange (1991) 51: Says he got five ohs for takin on the transportation job.
[UK]K. Koke ‘Fire in the Booth’ [lyrics] We’d probably all be broke if [we] don't slang / That’s why I'm shotting O’s on the road fam.
Young Jeezy ‘Me OK’ [lyrics] 34 a unit, nine hundred a O.
67 ‘Live Corn’ [lyrics] I'm still slanging these O’s, running through hoes.

2. (drugs) opium.

[US]D. Maurer ‘Junker Lingo’ in AS VIII:2 27: Opium is referred to specifically as O., mud, or hop, and the addict is known as a hophead, pipe-smoker, or cookie.
[US]W. Burroughs letter 5 May in Harris (1993) 83: Still smoke O once a week. It is different from needle kicks.
[US]Rigney & Smith Real Bohemia 58: It is a member of the opium alkaloid family – which includes opium (called ‘O’).
[US]T. Southern Blue Movie (1974) 206: The ‘long-ago-and-far-away’ glitter in her eyes reflected the double dose of liquid O-meth she had dropped for the occasion.
[US] in C. Browne Body Shop 28: Old men sittin’ round the villes smoking O.
[Aus]V. Viidikas ‘Island of Gems’ in India Ink (1984) 45: By the second packet of o. we are sweating profusely and being given bowls of cold tea.
[US](con. early 1950s) J. Ellroy L.A. Confidential 365: Lamar Hinton said Spade smoked opium; Spade played the Lariat Room in Frisco – across from Chrissie Renfro’s place of death. Chrissie died with ‘O’ in her system.
[US]ONDCP Street Terms 16: O — Opium.

3. (US drugs) a $50 rock of cocaine.

[US]T.R. Houser Central Sl.

4. (US drugs) an ounce of cannabis.

Chief Keef ‘No Tomorrow’ [lyrics] Lotta pound lotta O's / Lotta of bankrolls and clothes.

In compounds