Green’s Dictionary of Slang

bub n.1

also bubb, bubby, humming bub
[Lat. bibere, to drink]

[mid-17C–19C] drink, esp. strong beer; thus bub and grub, drink and food.

In compounds

In phrases

knock about the bub (v.)

[late 18C–mid-19C] to circulate the bottle, to pass the drink around.