Green’s Dictionary of Slang

rager n.

[rage v. (1)]
(Aus./N.Z./US campus)

1. a particularly good party.

[US] P. Munro Sl. U.
[US]Eble Campus Sl. Nov. 10: rager – large, out-of-control party.
[US]M. Lacher On the Bro’d 20: Mad wet T-shirt ragers.

2. (also rage) a person, or animal, known for wild behaviour.

[Aus]‘Rolf Boldrewood’ Colonial Reformer II 107: A livelier lot of ‘ragers’ I haven’t seen for many a day.
[Aus]‘Rolf Boldrewood’ In Bad Company 275: Father’s going on like an old ‘rager’ bullock.
[Ire](con. 1930s) J. Healy Death of an Irish Town 20: They were, in the current slang of the town, ‘the buff shams’, ‘rager coves’.
[Scot](con. mid-1960s) J. Patrick Glasgow Gang Observed 131: He’s a right rage, aw right.
[US] P. Munro Sl. U.
[NZ] McGill Reed Dict. of N.Z. Sl.