- (slang, dated) The greatest extent or degree of something; used in comparisons to indicate a superlative.
1901, Edith Nesbit, The Wouldbegoods, T. Fisher Unwin:
- "For the wooden fence leading up to the bridge had caught fire, and it was burning like billy oh."
1995, Marion Houldsworth, The Morning Side of the Hill, Boolarong Press:
- "'Our old saw's as blunt as billy-oh! You couldn't cut butter with it!'"