In Irish mythology, the sídhe (pronounced shee) are a supernatural race, quite distinct from humankind. There are a number of different types of sídhe: the sluagh sídhe, the fairy host or Wild Hunt, can fly through the air and shift shape at will, the sídhe who walk the earth at dusk and the guardian sídhe of the lakes of both Ireland and Scotland. Also the banshee.
They are the remnants of the underground kingdom given to the Tuatha Dé Danann after they were defeated by the Milesians. According to The Book of Invasions or Lebor Gabála Érenn, the Tuatha Dé Danann, the “People of the Goddess Danu” were defeated in battle by the mortal Sons of Mil. As part of the surrender terms the Túatha Dé Danann agreed to dwell underground in the síde (singular síd), the hills or mounds that dot the Irish landscape. Each member of the Tuatha De Danaan was given one mound. Later, due to a corruption of the meaning, both the mounds and the supernatural entities (i.e. sprites) became known as the síd, modern Irish sídhe.
The Sidhe had not reached the point of no return yet, there were still enough left on Maxim to be considered a viable race, but those of ancient minds as Azrael, also looked far into the future.
Perhaps her fellow Sidhe had simply hidden himself too well for her eyes and senses, maybe he had kept his movements so secret that not even the Voralphian tribe of Culaearien had been able to discover what he was up to.
There were few enough Sidhe in the isle as it was and it was good to know that, on this one day at least, their numbers had not decreased.
For people new to this term, Sidhe refers to the spirits known as the faeries, the Dananns, the old Irish gods and goddesses, and the Shining Ones; it also refers to the realm in the Otherworld where they reside.
The Sidhe (pronounced "shee") refers to both the world of Faerie and the spirits of that world, who are also known as the faeries, the Danann gods and goddesses, and the Shining Ones.
Spirits such as the Sidhe seem to survive the great changes in the Earth, and return or disappear, to the extent that their power is needed in ordinary reality.