Etymology 1

The hat sense derives from Charles Baillie, 2nd Baron Lamington, who was governor of Queensland from 1896 to 1901. (Reference: Sidney J. Baker, The Australian Language, second edition, 1966, page 272) Apparently Lamington liked to wear such a hat.

Etymology 2

The cake sense is uncertain. Although current dictionaries all associate it with the Baron, the earliest publication of this derivation is by John Hepworth in Nation Review July 1977. Baker’s earlier book gives the cake (page 86) but doesn’t associate it with the Baron, suggesting the theory wasn’t current in the 1960s. (Reference: Australian National University OzWords May 1999.)

Noun

1. A small square Australian cake made with sponge cake covered on all sides (including top and bottom) with chocolate and desiccated coconut.