Green’s Dictionary of Slang

1. (Aus./N.Z.) an assistant, a helper.

1871		Wkly Times (Melbourne) 8 Apr. 3/3: I got on very well with him, and was often his off-sider.
1887		Queensland Figaro (Brisbane) 12 Mar. 13/1: The bullock waggon was slowly moving out of the township [...] ‘Hang it all, Bill,’ said the off-sider when they came to the first halt, ‘that rum has almost killed me’.
1890		Bulletin (Sydney) 5 July 13/3: How would the bullock-driver get on if there was nothing but gentlemanly language in existence, and he couldn’t dash the off-sider, and tell him to mind where he was going if he didn’t want his gory horn knocked off his profane head and the rest of his condemned carcase banged to -- -- -- --?
1894		G. Boothby On the Wallaby 219: Talking of bullock drivers, the driver himself is called the bullocky, while his mate or assistant is denominated the bullocky’s offsider.
1903		J. Furphy Such is Life 184: Sort o’ off-sider for a gang o’ Chinks!
1919		Aussie (France) XII Mar. 1/2: Joe, by the way, is our babbler’s offsider.
1924		Worker (Brisbane) 25 Sept. 16/3: Who pay’s fare of Cook’s offisder?
1939		Franklin & Cusack Pioneers on Parade 153: Come for me again if you want an off-sider. I’m sorry I don’t know much about nursing.
1940		(con. 1870s) E.C. Studholme Te Waimate (1954) 127: 1 cook’s mate, generally known as the offsider or ‘slushy’.
1951		(con. 1941) E. Lambert Twenty Thousand Thieves 149: He had only held this job because his off-sider was an honest and conscientious cook.
1966		P. Pinney Restless Men 114: ‘What’re you doing now?’ ‘Plasterer’s offsider.’.
1970		Aus. Women’s Wkly 4 Mar. 53/1: three weeks as shearer’s offsider [...] and chief cook and bottle-washer.
1973		(con. 1930s) F. Huelin ‘Keep Moving’ 6: ‘Hi! Charlie,’ he called to his offsider, ‘how long since we did the Echuca run?’.
1985		R.G. Barrett You Wouldn’t Be Dead for Quids (1989) 16: His offsider on the door of the Kelly Club was leaving.
1996		(con. 1964-65) B. Thorpe Sex and Thugs and Rock ’n’ Roll 132: Natasha, Boris’s offsider in the ‘Rocky and Bullwinkle’ cartoons.
2005		M.B. ‘Chopper’ Read Chopper 4 112: Damien Bugg [...] was in attendance with his ever ready legal offsider, Miss C.J. Geason.
2018		G. Disher Kill Shot [ebook] The staffer, young, glanced at her offsider.
2021		C. Hammer Opal Country 45: ‘Used to be his offsider [...] Then he sacked him’.

2. attrib. use of sense 1.

1915

F. Garrett diary 23 Nov. 🌐 Arthur Schofield gone with jaundice. Lot of it about. Scottie has gone offsider cook.