Green’s Dictionary of Slang

(Aus.) quiet, silence.

1949		L. Glassop Lucky Palmer 171: Gents [...] a bit of shoosh, please gents.
1986		R. Beckett Dinkum Aussie Dict. 46: Shoosh: A demand for an audience to shut up, as in, ‘Let’s have a bit of shoosh, ladies and gents.’.