Green’s Dictionary of Slang

once n.2

1. in pl., wages [they come once a week].

[UK]J. Ware Passing Eng. of the Victorian Era.

2. £1, a £1 note [oncer n. (2)].

[UK]F. Norman Bang To Rights 121: The geezer [...] had told him that if he went bent he would give him three onces.