Green’s Dictionary of Slang

(S.Afr.) a general excl.

1942		U. Krige Dream and Desert (1953) 121: ‘Jysis!’ Mos-tert whistled through his teeth. ‘I had no idea they’d collect such a packet.’ [DSAE].
1955		D.C. Themba in Crwys-Williams S. Afr. Despatches (1989) 320: Yessus! The Leech will never find us here [DSAE].
1969		A. Fugard Boesman and Lena Act II: It was big! All the roads [...] new ways, new places. Yessus! It made me drunk.
1977		D. Muller Whitey 100: ‘Yissis!’ Achmet Smit gave a loud cry as he tumbled from the bench to land on all fours.
1982		C. Hope Private Parts 9: Jissus, but it’s hot.
1982		P. Slabolepszy Sat. Night at the Palace (1985) 55: Yassas! You bliksem! [Ibid.] 62: Shassas, you know!
1999		Indep. on Sun. 1 Aug. 16: Yissus: Used to express astonishment or annoyance.