Green’s Dictionary of Slang

rosiner n.

also rossiner, rozener, rozner, rozziner
[Irish 20C+; Aus. 1930s+; rosin n. (1) + sfx -er]

1. (Aus./Irish) any form of stiff drink, a pick-me-up.

[Ire]L. Doyle Ballygullion 186: The wee man poured himself out a rozener would ha’ have made a cat spake.
[Ire]S. Beckett More Pricks than Kicks 119: ‘And the rosiner,’ said Mrs Tough, ‘will you have that in the lave too?’.
[Ire]‘Myles na gCopaleen’ Faustus Kelly in ‘Flann O’Brien’ Stories & Plays (1973) 123: Mr Kelly is having a few rossiners down the way.
[Ire]L. Doyle Back to Ballygullion 134: We went into Barney’s to have a farewell rozener!
[Ire](con. 1940s) B. Behan Confessions 105: My cousin is a decent skin [...] and in event he was taking me for a rosiner.
[Aus]B. Wannan Folklore of the Aus. Pub 128: Roziner; Rozner: strong drink; any stiff tot of spirits.
[Ire]B. Behan ‘The Last of Mrs Murphy’ in After the Wake 20: Going past a pub on the corner of Eccles Street [...] My granny and Long Byrne and Lizzie MacCann all said they’d be the better of a rozziner.

2. (Aus.) something of worth, a profitable bargain.

[Aus]J. Byrell (con. 1959) Up the Cross 104: The Kraut bought him at a rosiner of a price.
[Aus]J. Byrell Lairs, Urgers & Coat-Tuggers 71: ‘Only half a friggin’ furlong left. Shit! You’re goin’ ter get ‘im! Got ‘im! You little rosiner!’ [ibid.] 218: And the 1974 Doncaster day [...] was about-turned into a real rosiner when Tontonan brought home the bacon.