Green’s Dictionary of Slang

dot n.3

1. in pl., money [? SE dot, a dowry].

[US]Matsell Vocabulum.
[US]Trumble Sl. Dict. (1890).
[UK]Partridge DSUE (1984) 333/2: from ca. 1880.

2. (UK Und.) in pl., piano keys.

[US](con. 1910–20s) D. Mackenzie Hell’s Kitchen 118: Dots ... piano keys.

In compounds