Nixer

2000, Patricia Scanlan, City Lives, Random House (Bantam Books), page 385, 'Ciara, you were getting very well paid. Over the odds in fact. And doing the odd nixer is a hell of a lot different from defrauding your employers,' Devlin retorted angrily.

Source: wiktionary

2002 [Ashgate Publishing], Ullrich Kockel, Regional Culture and Economic Development, 2017, Taylor & Francis (Routledge), page 51, Although this advice was given with a view to allowing Séamus to continue in farming while maintaining his factory job, the success of this innovation, which was largely financed by savings facilitated through ‘nixers’ and poteen sales – was such that Séamus quit his job, and is now enjoying a higher level of total income than before: His flock productivity has almost doubled, and quality improved considerably as the weaning rate rose.

Source: wiktionary

2024, Seamus O'Rourke, Leaning on Gates, Gill (Gill Books), unnumbered page, He asked me if I was interested in doing a nixer. I didn't know what a nixer was. I was so sheltered in my little safe nine-to-five working world that I didn't realise there was another world out there with less emphasis on clock-watching and more on making money. 'A nixer – a couple of evenings' work for cash.' 'Oh,' I said, 'that sounds good to me.'

Source: wiktionary