Green’s Dictionary of Slang

something or someone excellent, first-rate.

1904		Sydney Sportsman 18 May 6/1: Yank Pearl and Fred Watson should pack the Newtown Pastime Club [...] It will be a boshter and cush and all, likewise ribuck and a boskerina!
1915		Aus. Worker (Sydney) 30 Dec. 12/2: ‘Go it, you corker! Let him have it all, you beauty! Oh, you boskerina! Mind his left, Dud!’.
1916		Sydney Sportsman 6 Dec. 1/8: Stellarine [i.e. a racehorse] is a boskerina that punter a should not let dodge ’em.
1932		Braidwood Dispatch (NSW) 9 Sept. 1/2: Knowin’ the ropes, I dives out, and is back in a tick with the music-box. Spillin’ it on the bed, I opens up an’ gives them me old favorite, the Boskerina Waltz.