oncer

plural oncers

1. historicalinformalA one-pound note.

   1 more example

   On whatever point Jane’s eyes rested, through whichever line her gaze ran, she saw cheques being signed, credit-card counterfoils being scrawled across, standing orders being arranged, and cash – wholesome dosh, ponies, monkies, oncers, coins of the realm – flowing around like mercury, like some element.

   1993, Will Self, My Idea of Fun

2. poeticA person who does something once.

   Could he but once see Nature as / In truth she is for ever, / What oncer would not fall in love?

   1944, W. H. Auden, The Sea and the Mirror: A Commentary on Shakespeare's The Tempest, Part 1. Prospero to Ariel

3. informalA single sexual encounter between two individuals, a one-night stand.
4. informalA person with whom one shares a single sexual encounter, a one-night stand.

plural Oncers

1. slanglifestyleA fan of the television series Once Upon a Time.

   A horde of 'Oncers' from all over the continent are descending on little Steveston/Storybrooke this weekend.

   2015 October 2, “Contents”, in Richmond News, page A3

   2 more examples

   And fun because, well, he gets to interact with “Oncers” at fan events like PaleyFest and Comic Con […]

   2013 June, Hiko Mitsuzuka, “Charmed & Generous: Josh Dallas”, in Bello, number 47, page 14

   Katy Lewis, a resident of Whitehorse, Yukon, is a 'Oncer'—a super fan of the popular TV show Once Upon a Time.

   2014, Matthew Hoekstra, "Once draws super fans to Steveston", The Richmond Review, 21 March 2014, page 1 (image caption)