Green’s Dictionary of Slang

bob v.1

[OF bober, to deceive. SE to late 17C and found as such in Shakespeare]

1. [early 16C–early 19C] (UK Und.) to cheat, to deceive; thus bobbed, cheated; bobber, a cheat.

2. [mid-17C-18C] to thrash, to beat; thus bob(bed), beaten.

3. [mid-19C] (UK) to adulterate milk with water.

4. [late 19C] to wound or kill.