Green’s Dictionary of Slang

caroline n.

(Irish) a style of tall hat.

1879		C.J. Kickham Knocknagow 155: He took off his hat and swung it downwards to shake off the wet with which the fur – for it was a beaver or ‘Caroline’ – was dabbled.
1943		(con. 1850–60s) G.A. Little Malachi Horan Remembers 14: When he dressed himself he would wear the felt half-tall hat which was known here as ‘a nailer’s chimney’ (Another name for [it] was a ‘caroline hat’).

In phrases

she could hurl under the bed with a caroline hat on

(Irish) used of a woman who is very short.

2012

www.slang.ie 🌐 Biddy Maguire is so small she could hurl under a bed with a caroline hat on.