rhubarb, n.³ — Green’s Dictionary of Slang

rhubarb n.³

[rhy. sl.; rhubarb = sub n.¹ (5); (Cockney pron. ‘roobub’)]

an advance on one’s wages.

1929		F.C. Bowen Sea Sl.
1937–84		Partridge DSUE.
1960		J. Franklyn Dict. Rhy. Sl.
1972		Dodson & Saczek Dict. of Cockney Rhy. Sl.
1992		R. Puxley Cockney Rabbit.