Green’s Dictionary of Slang

one v.

(Aus. gambling ) to throw a head and a tail, i.e. one of each side of the coin, in two-up.

[Aus]J. Holledge Great Aust. Gamble 101: If the pennies are different - showing one tail and one head - it is classed as a no throw, and the cry is: ‘He’s oned ‘em’.