Green’s Dictionary of Slang

five-pound (of money).

1847		A. Smith Natural History of the Gent 5: The guvner give a fippun note for that little mare.
1848		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?
1855		J. Brougham Basket of Chips 158: Only a paltry fip-poun ten.
1880		J. Payn Confidential Agent II 193: I never saw no fippund notes so clean as this.