(leetspeak) Used instead of ! to amplify an exclamation, parodying unskilled typists who forget to press the shift key while typing exclamation points, thus typing "1".
“Perhaps you think that football has told him in no uncertain terms that you can't have what you want just for the asking and a hundred million used oncers.”
“Words like notes, ackers, pelf, readies, smackers, bills, oncers, and so many more spring to mind.”
“Meanwhile, many Oncers are still reeling from the shock of a character's death.”