(Originally) a kind of straw hat with a wide brim, fashionable in the late 19th cent. (now rare); (later) a tall, brimless hat which widens towards a flat, disc-shaped top, traditionally worn by married Zulu women.
The traditional hat is called isicholo in Zulu.
1879
Hyam's stock of Straw Hats for men, boys, and Children, is very large and varied in styles; his Zulu Hats, at Threepence halfpenny, are astonishing.
Freeman's Journal (Dublin) 31 May 1/3
1893
She had managed, while seizing a Zulu hat, to divest herself of the apron.
C. M. Yonge & C. R. Coleridge, Strolling Players viii. 54
1941
Both [children] wore what were then known as Zulu hats, plaited of rushes and very wide brimmed.
F. Thompson, Over to Candleford x. 144
1994
The vivid red Zulu hat also tells us to see something about the wearer.
Calgary (Alberta) Herald (Nexis) 29 March b6
2012
A middle-aged woman, a formidable-looking Rasta in a giant Zulu hat, joined her.