sídhe

Sídhe, often anglicized as Sidhe, is a Gaelic term referring to the supernatural inhabitants of the Otherworld in Irish and Scottish folklore. The word literally denotes a mound or hill, and in tradition the sídhe are commonly identified with the Aos Sí, the People of the Sídhe, a race of fairies or fairy-people.

The sídhe are said to dwell in or beneath landscapes associated with ancient mounds, hills, and enclosures known as sith or sidhe. They are portrayed as powerful, long‑lived beings with magical abilities, capable of blessing or cursing humans, shaping events, or luring travelers with music or beauty. Interactions with mortals typically occur at twilight, at boundary areas between worlds, or within fairy mounds, and are often mediated by offerings, respectful behavior, or warnings to avoid crossing thresholds, staying too long, or eating fairy food.

In Irish mythology the Tuatha Dé Danann, a legendary people, are said to have retreated into the sídhe after defeat by the Milesians, becoming the Aos Sí. This linkage anchors the sídhe in the broader conception of the Otherworld and the landscape as a liminal space.

In contemporary usage, sídhe denotes the fairy folk in folklore and fantasy literature, and the term appears in cultural place names, scholarly works, and popular media. Beliefs regarding the sídhe vary by region, but they are consistently treated as a bridge between the living world and a magical otherworld.