Green’s Dictionary of Slang

1. (Aus.) alcohol, esp. beer.

1906

E. Dyson Fact’ry ’Ands 181: ’Ow’d I iv bin many er time if ’twasn’t fer ther drop iv buck-up?

2. encouragement, cheering up.

1912

Bulletin (Sydney) 17 Oct. 13/4: I have encountered three similar excitements, and on each occasion the Church was in low water at the time, and sadly in need of a spiritual buck-up.

3. (W.I.) a social gathering, for no specific purpose other than enjoyment.

1956

cited in Cassidy & LePage Dict. Jam. Eng. (1980).