Green’s Dictionary of Slang

1. any top quality drug.

2010		(con. 1967) K. Richards Life 200: Robert really liked to get stoned, ‘wonderful hashish,’ ‘Afghani primo’.
2010		K. Richards Life 231: The best hash [...] was Afghani primo, which used to come in two shapes: like flying saucers, with a seal on it, or in the shape of a sandal.
2013		K. Shea ‘Having Chiqui’ in ThugLit July-Aug. [ebook] She asked Muzz over to her basement apartment to score some primo[i.e. marijuana].

2. (also primo square) a marijuana cigarette laced with cocaine and/or heroin.

1985		T.R. Houser Central Sl. 42: primo Marijuana with cocaine mixed in it.
1989		P. Munro Sl. U.
1997		G. Sikes 8 Ball Chicks (1998) 54: He lit a joint, sticking it under my nose to make sure I knew it was weed — ‘herbal,’ as he called it, not a ‘primo’ laced with cocaine.
2000		Ebonics Primer at www.dolemite.com 🌐 primo Definition: joint laced with cocaine Example: Leroy been smokin’ dem primos again. He lookin’ all gacked up.
2001		ONDCP Street Terms 17: Primo square — A marijuana joint laced with crack.