Green’s Dictionary of Slang

1. thunder.

1998		R. Puxley Fresh Rabbit.
2002		B. Kirkpatrick Wicked Cockney Rhy. Sl.

2. (Aus.) an act of vomiting.

1992		R.G. Barrett White Shoes 86: Have you ever heard of the expression ‘Having an up and under’? [...] A technicolor yawn? Having a laugh at the footpath?
2016		N. Cummins Adventures of the Honey Badger [ebook] VITAL AUSSIE VERNACULAR Vomit: 1. Up and under 2. Chunder 3. The technicolour yawn 4. Barking at the lawn 5. Driving the porcelain bus.
2021		Betoota-isms 252: ‘Kelly must’ve have had a raw prawn out on the boat, first thing I heard [...] was her in the bathroom having an Up ’n’ Under’.