Green’s Dictionary of Slang

boss up! excl.

[calque f. Cape Du. pas op! look out!]

(S.Afr.) take care! look out!

Show quotations
T.H. Bowker diary 7 Aug. n.p.: They fired a kafir fire in the top of the Clugh where the blackguards are watching us, boss up [DSAE].
Nicoll & Eglinton The Sportman in S. Afr. 81: Wherefore extra precautions should be observed, or as the Dutch hunters say, boss up.
[SA]C. Pettman Africanderisms 83: Boss up! A corruption of the Cape Dutch Pas op! – Take care! look out!