‘‘The long-haired one,’’ from the Gaelic gruag, a wig. The
gruagach was a fairy being with protective duties in Scottish legends,
apparently of either sex, but generally female. The gruagach
was particularly associated with cattle, and milk was laid
aside for him or her every evening—otherwise no milk would
be given at the next milking. Usually this being was of a beneficent
nature, although it occasionally made mischief by loosing
the cattle so that the herders had to get up, sometimes several
times during a night, to tie them up. This apparently caused
the gruagach much impish delight.
Among the many stories of fairies, there are tales in different
parts of Scotland about the gruagach. It seems that this fairy
commonly had long hair and was well dressed, whichever sex
it happened to be.
Thompson, Francis. The Supernatural Highland. London
Robert Hale, 1976.