Green’s Dictionary of Slang

(S.Afr.) a servile, subservient black person.

1972		Drum (Johannesburg) 8 Aug. 8: In Saso lingo a non-White is regarded as a Ja-Baas, a sell-out [AND].
1980		E. Joubert Poppie Nongena 378 : Ja, they say, you are the ja-baas, the yes-men, so they don’t trust us no more. They say the whites tread on us [AND].
1989		Pace Dec. 4: The leadership position is for the learned and not for bo ‘Dom Jan’ and bo ‘Ja Baas’ [AND].