1 a five-pound note 20.
2 a pound note; any banknote 20. Compare deuce flimsies etymology: onomatopoeic; attested as ‘slang a bank note; also, paper money’ in the early nineteenth century; attested by Galloway Tinkler-Gypsies note:
Grose and Egan (1823) attest the form flimseys ‘bank notes’ as ‘Cant’.