Green’s Dictionary of Slang

grub v.1

[grub n.2 (1) + SE grub up, to uproot, i.e. whatever can be found/begged]

1. [18C+] (also grub out, grub up) to eat; thus grub and bub, to eat and drink.

2. [19C–1920s] to provide with food.

3. [late 19C] to scavenge.

4. [late 19C+] to beg, to scrounge; thus on the grub.