Green’s Dictionary of Slang

1. the favourite prostitute among those a pimp controls.

1958		Murtagh & Harris Cast the First Stone 25: The girls didn’t know which one he regarded as his main chick.
1972		E. Folb Urban Black Argot 142: Main Whore [...] ii. a pimp’s number one money-making prostitute.
1972		(con. 1950s) D. Goines Whoreson 83: First of all your main lady is a bull-dyker.
1977		J.L. Dillard Lex. Black Eng. 88: The most trusted one – often the oldest in his service and not necessarily the most beautiful or the favorite – is the bottom whore, bottom woman, bottom bitch, or main lady and is given a certain amount of authority over her ‘sisters.’ She is also sometimes called Mother.
1979		‘Iceberg Slim’ Airtight Willie and Me 112: Red’s main bitch is a super fox.
1981		A.K. Shulman On the Stroll 109: You could spend all your time on your main lady — making the necessary appearances on the stroll and in the bars.

2. a man’s favourite girlfriend.

1964		R. Abrahams Deep Down In The Jungle 154: He told his main whore he had to go, / Down to the coconut grove to the water hole. [Ibid.] 266: Main who’ – Best girl friend.
1964		‘Return of Honky-Tonk Bud’ in D. Wepman et al. Life (1976) 62: Four went to men and a limp-wrist friend, / And the fifth went to his main girl.
1972		E. Folb Urban Black Argot 142: Main Stuff one’s best friend; one’s primary girl friend.
1972		E. Folb Urban Black Argot 142: Main Whore i. one’s main woman — sexually, romantically or both.
1980		E. Folb Runnin’ Down Some Lines 142: Terms for a sexually attractive woman are all shared with the pimp – main ’ho, main bitch. [Ibid.] 143: Terms that are used interchangeably to characterize a sexually attractive woman and a variety of drugs [...] main stuff.
2000		W.T. Vollmann Royal Family 497: The tall man had the number of the O.G.’s main bitch, [...] who’d never turned a trick in her life.

3. a preferred female friend.

2000

W.D. Myers ‘Block Party–145th Street Style’ in 145th Street 145: ‘Right, so now J.T.’s mad at me, and I hurt my moms, and now my main girl is hurt, too’ .