one out, adj. — Green’s Dictionary of Slang

one out adj.

(Aus.) alone; thus two-out, with a single accomplice or helper; ten out, in a team or gang of 10 etc.

1974		Adamson & Hanford Zimmer’s Essay 71: The one-out peters of Maitland Gaol are plumbed.
1977		H. Garner Monkey Grip 212: Neither of us will ever be one-out while the other’s alive!
1984		B. Ellem Doing Time 108: The best way to survive is to be one-out.
1990		Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 One-out. 1. To be in a single cell.
1993		Smith & Noble Neddy (1998) 303: I felt sorry for Richard being one-out [by himself] at a time like this. You need someone to talk to on your first night in the cells.
2000–02		Macquarie Dict. 🌐 one [...] adverb 5. Criminal (used with a specifying number) in a group of that number; thus one out – alone, two out – in company with another, five out – in a group of five, etc.

one-out fight (n.) [one person comes out of the group]

(Aus. teen) a fight between the two champions of a pair of rival teen gangs.

1965		W. Dick Bunch of Ratbags 132: I was still getting involved in one-out fights and gang-wars.
1984		Partridge DSUE (8th edn) 832/1: since ca. 1925.
2004		(con. 1960s-70s) T. Taylor Top Fellas 26/1: If you had a beef with someone you’d settle the matter with a fair-square one-out fistfight.

go one-out (v.)

(Aus.) to act as an individual (as opposed to a team).

1992

M. Coleman Fatty 153: ‘Everyone thought they were big stars and all we had to do was to show up. They were going one out’.