Green’s Dictionary of Slang

(Ling. Fr./Polari) a sovereign, £1 sterling.

1859, 1860		Hotten Dict. of Modern Sl. etc.
1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict.
1895		C. Crowe Aus. Sl. Dict. 60: Poona, a sovereign.
1901		Argus (Melbourne) 20 Sept. 6/4: A sovereign is [...] a goldfinch, a dragoon, a king s picture, a poona, or a thick ’un.
1925		Western Mail (Perth) 28 May 21/1: [from Daily Mail, London] A sovereign had a lot of slang names [...] a portrait, a yellow boy, [...] a foont, a poona [and] a bean.