Wikipedia
The glaistig is a ghost from Scottish mythology, a type of fuath. It is also known as maighdean uaine (Green Maiden), and may appear as a woman of beautiful or monstrous mien, as a half-woman half-goat similar to a faun, or in the shape of a goat. The lower goat half of her hybrid form is usually disguised by a long, flowing green robe or dress, and the woman often appears grey with long yellow hair.
The name is evidently cognate with the Manx " glashtin", and is similar to the "sacbaun" of Galloway. She is also known as "Green Jean".
Usage examples of "glaistig".
She”—he nodded toward the woman in the pool—“is a glaistig, and so you may call her.
All that water reminded her of the Peavey Plaza fountain, and the glaistig with her cold voice and ominous little fangs.
The glaistig, for one, would laugh herself ill, but I know you wouldn’t care about that.