sidhe

In Irish mythology the aos sí (older form, aes sídhe), pronounced "ess shee", are a powerful, supernatural race comparable to the fairies or elves of other traditions. They are variously believed to live underground in the fairy mounds, across the western sea, or in an invisible world that coexists with the world of humans.

In the Gaelic languages, the "people of the mounds" are also referred to in Irish as the daoine sídhe ("deena shee"), and in Scottish Gaelic as the daoine sìth or daoine sìdh. They are variously believed to be the ancestors, the spirits of nature, or the goddesses and gods themselves.

_Wikipedia