Green’s Dictionary of Slang

fip-poun n.

also fippund, fip pun, fippun
[elision of SE]

five-pound (of money).

[UK]A. Smith Natural History of the Gent 5: The guvner give a fippun note for that little mare.
[Aus]Bell’s Life in Sydney 26 Aug. 2/5: If so be as you ever nicks another fip pun not in mistake, just be kind enough to bring the hexpence of defindin it vith yer, will yer?
[US]J. Brougham Basket of Chips 158: Only a paltry fip-poun ten.
[UK]J. Payn Confidential Agent II 193: I never saw no fippund notes so clean as this.