Green’s Dictionary of Slang

loose n.

(Aus.) an evening party.

1871

Hamilton Spectator (Vic.) 7 Jan. 1/7: If asked to an evening party, it is a ‘loose’, a ‘blowout’.

SE in slang uses

In phrases

make a loose (v.)

to make one’s escape.

1709

N. Ward Secret Hist. of Clubs 165: A Lawyer’s Clark, who had venturd to make a Loose from the Finger Drudgery of Pen Ink and Paper, would usher in the Buxom Daughter.