Green’s Dictionary of Slang

1. (UK Und., also cow’s licker) £1 [= nicker n.² (1)].

1984

Partridge DSUE (8th edn) 261/2: cow’s licker £1.

2. prison [= nick n.³ (2a)].

1972		Dodson & Saczek Dict. of Cockney Rhy. Sl. 26: cow’s lick. Nick.
1992		R. Puxley Cockney Rabbit.
2002		B. Kirkpatrick Wicked Cockney Rhy. Sl.