Green’s Dictionary of Slang

1. the penis.

1890–1904

Farmer & Henley Sl. and Its Analogues.

2. (US, also pahtner) a friend (cf. pard n.).

1935		N. Algren ‘A Lumpen’ in Entrapment (2009) 33: Partner, I’ll have one of them little books.
1968		‘Sl. of Watts’ in Current Sl. III:2.
1977		A. Hoffman Property Of (1978) 76: If you’re buying, partner [...] I’ll have whiskey and water.
1980		E. Folb Runnin’ Down Some Lines 249: partner 1. Good friend. 2. Street companion. 3. Acquaintance (takes it [sic] meaning and force from context).
1992		Bentley & Corbett Prison Sl. 39: Pahtner A close friend. A pahtner may also be a business associate or a workmate.
1997–2001		Online Sl. Dict. 🌐 partner n 1. friend. Pronounced ‘pot-na’. (‘Me an my partner gonna bounce.’).