(Celticmythology) A malevolentshapeshifting spirit, most often in the form of ahorse, believed to haunt the rivers and lochs of Scotland.
1828, James Hogg,The Brownie of the Black Haggs:
He was a boy in form, and an antediluvian in feature. Some thought he was a mule, between a Jew and an ape; some a wizard, some akelpie, or a fairy, but most of all, that he was really and truly a Brownie.