Green’s Dictionary of Slang

the number five.

1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor I 411/2: There’s people there talk backward – for one they say eno [...] for five evif.
1870		Hotten Sl. Dict.
1885		Edinburgh Eve. News 26 Dec. 3/5: ‘Eno’ is one; ‘owt,’ two; ‘eerth,’ three; ‘rouaf,’ four; ‘exif,’ five; and ‘xis’ pronounced exes, six.
1953		J. Franklyn Cockney 297: Ewif (five).