Green’s Dictionary of Slang

Saturday n.

SE in slang uses

In compounds

Saturday gangster (n.)

(Aus. Und.) an aspirant gangster.

[Aus]Smith & Noble Neddy (1998) 154: This particular night they were all there, including Terry Ball (a real nutter), Roy Thurgar (a very good boxer) and that old Saturday [would-be] gangster Billy Stevens.
Saturday-night (n.)

wages.

[UK]G.F. Northall Warwickshire Word-Book 199: Saturday-night. Wages. ‘If I have a good Saturday-night, I’ll buy the nipper a pair o’ boots.’ ‘Have you drawed your Saturday-night?’.

In phrases

Saturday-to-Monday (n.)

a mistress whom one sees only at weekends.

[UK]A. Binstead Pitcher in Paradise 37: Something very choice that he was taking down to ‘Saturday-to-Monday’ at the Pavilion.
shitten Saturday (n.) [mispron. of SE shut-in Saturday, referring to the day on which Christ’s body was enclosed in his tomb]

(mainly school/provincial) Easter Saturday.

[UK]Hotten Dict. of Modern Sl. etc.
[UK]Hotten Sl. Dict.