Green’s Dictionary of Slang

billy-o n.

[-o sfx (7)]

1. [late 19C+] (also billyho, billy-ho, billy-oh) euph. for hell, thus trouble, punishment.

2. [1910s] nonsense, rubbish.

In phrases

like billy-o (adv.) (also like billyho, …billy-ho, ...billy hell, ...billy-oh, ...(the) billyo) [dial., euph. for ‘bloody hell’]

[mid-19C+] a general intensifier and expression of energy or effort, most enthusiastically, strenuously, speedily.