Definition of "leghorn"

When straw-hats had become unfashionable, Mrs. Nollekens hinted to old White, the hatter […] , that possibly he could accommodate her with a Leghorn hat at a moderate rate.

1828, JT Smith, Nollekens and His Times, Century Hutchinson, published 1986, page 65

The difference between the two classifications has always been intended to cover unblocked and untrimmed hat bodies, such as panamas, bangkoks, and leghorns, and other hats which are woven by the natives in South American and oriental countries where they are produced.

1918, Schedules M and N, free list, customs administration and income tax; subject index, page 1515