Definition of billy-o in English:

billy-o

noun

British
informal
  • Very much, hard, or strongly.

    ‘I had to run like billy-o’
    • ‘This little beauty's older than I am, but it still reads and writes like billy-o.’
    • ‘Is that the same stuff as the algae that kills all the marine life under it and breeds like billy-o?’
    • ‘He would spend a while trying to get the chute to catch the wind, and then run like billy-o down the hill, occasionally jumping in the air.’
    • ‘But only to Claus Jensen, who nearly restores some Danish pride with an exquisite chip from the edge of the area that nearly beats Seaman, who tips the ball over the bar with his midlife-crisis mane flapping like billy-o.’
    quickly, fast, swiftly, speedily, at speed, at full speed, at the speed of light, post-haste, hotfoot, at full tilt, as fast as one's legs can carry one, at a gallop, expeditiously, briskly, promptly
    View synonyms

Origin

Late 19th century: of unknown origin.

Pronunciation:

billy-o

/ˈbɪlɪəʊ/