Green’s Dictionary of Slang

1. (Aus.) a spree, any form of merry-making.

1948		R. Park Harp in South 79: ‘[I]t does a man no harm to have a bit of a gee-up now and again’.
2004		R.G. Barrett Rosa Marie’s Baby (2013) [ebook] It’s some sort of gee-up.

2. a false alarm.

1986		R.G. Barrett Godson 201: [T]he big inbred was mostly bluff, this was a gee-up and he wasn’t all that keen to fight anybody.
1998		R.G. Barrett Goodoo Goodoo 95: Norton’ instinct [...] told him this was a gee up.
1999		R.G. Barrett Wind & Monkey (2013) [ebook] It was all just a gee-up.

3. (Aus.) an act of encouragement.

1992		M. Coleman Fatty 175: And besides, what others might see as being in questionable taste at best, Lewis and Vautin laugh off as ‘gee-ups’.
2013		T. Peacock More You Bet 8: Stirring someone up might have been described as a ‘gee-up’.