The aos sí (pronounced [iːsˠ ˈʃiː]; English approximation: /iː s ˈʃiː/ eess SHEE; older form: aes sídhe, áes sídhe [eːsˠ ˈʃiːə]) are magical beings in Irish folklore. They are similar to elves and are believed to have come from the Tuatha Dé Danann, the gods of Irish mythology.

The name "aos sí" means "folk of the sí," referring to burial mounds where they are said to live. These mounds are considered entrances to another world, often called the Otherworld. In English, these places are sometimes called "shee," "fairy mounds," "elf mounds," or "hollow hills." The aos sí are said to live in these mounds and sometimes interact with humans. They are described as ancestors, nature spirits, or gods and goddesses.

In modern Irish, they are also called "daoine sidhe" (or "daoine sídhe") or "daoine sí." In Scottish Gaelic, they are called "daoine sìth," meaning "folk of the fairy mounds."

Etymology

In the Irish language, the word "aos sí" (or "aes sídhe" in older forms) means "people of the fairy mounds." In Old Irish, it was written as "áes síde." The word "sí" or "sídh" in Irish refers to a fairy mound or an ancient burial mound, which were believed to be entrances to an Otherworld. This word comes from the ancient Celtic language *sīdos, meaning "abode." It is related to the English words "seat" and "settle."

David Fitzgerald suggested that the word "sídh" might mean the same as "immortal." He compared it to words like "sídsat" (meaning "they wait/remain"), "síthbeo" (meaning "lasting"), "sídhbuan" (meaning "perpetual"), and "sídhbe" (meaning "long life"). In most stories about the sí, the idea of living a very long life or being ageless is often shown.

In medieval literature

In medieval Irish literature, the names aes síde and fír síde (folk of the síd) are the same as the terms Tuath Dé and Tuatha Dé Danann. The only difference is that Tuath Dé is often used in stories about the past and myths.

In the 7th century, the Irish bishop Tírechán described the sídh folk as "earthly gods" (Latin: dei terreni). The 8th century Fiacc's Hymn states that the Irish worshipped the sídh folk before Saint Patrick arrived.

In Irish folklore

Because Irish folklore was passed down through stories, the exact origins of the fairies are not clearly known. There are enough stories to suggest two possible origins. The fairies could be fallen angels or the descendants of the Tuatha Dé Danann; in the latter case, this is the same as aos sí. In the former case, it is said that the fairies are angels who fell from heaven, but whose sins were not serious enough to be sent to hell.

In many Gaelic tales, the aos sí are later versions of the Tuatha Dé Danann ("People of the Goddess Danu")—the gods and ancestors of Irish mythology. Some sources describe them as survivors of the Tuatha Dé Danann who moved to the Otherworld when fleeing the mortal Sons of Míl Espáine, who came from Iberia. As part of their agreement to surrender to the Milesians, the Tuatha Dé Danann agreed to retreat and live underground.

In folk beliefs, the aos sí are often given offerings to keep them happy, and people avoid actions that might anger them. They are rarely named directly but are called "The Good Neighbors," "The Fair Folk," or "The Folk." Their names, such as aos sí, aes sídhe, daoine sídhe (singular: duine sídhe), and daoine sìth, mean "people of the mounds," referring to the sídhe. The aos sí are generally described as very beautiful, though they can also be frightening and ugly.

The aos sí are seen as strong protectors of their homes—whether a fairy hill, a fairy ring, a special tree (often a whitethorn), or a loch or wood. It is believed that entering these spaces may cause the aos sí to take action to remove intruders. These stories are linked to the changeling myth in European folklore, where the aos sí are said to take people or replace children with changelings as punishment. The aos sí are often connected to certain times of year and hours, as the Gaelic Otherworld is believed to be closer to the mortal world at dusk and dawn. Festivals like Samhain, Bealtaine, and Midsummer are also associated with the aos sí.

A sídh (anglicized "shee") is a burial mound (tumuli) linked to the aos sí. In modern Irish, the word is "sí" (plural: "síthe"); in Scottish Gaelic, it is "sìth" (plural: "sìthean"); in Old Irish, it is "síd" (plural: "síde"). These sídhe are called "fairy mounds," "elf mounds," or "hollow hills" in English.

In some later English texts, the word "sídhe" is incorrectly used for both the mounds and the people who live in them. For example, W. B. Yeats, writing in 1908, called the aos sí simply "the sídhe." However, in older texts, "sidh" refers specifically to the homes, courts, or halls of the otherworldly beings who are believed to live there.

The aos sí are known by many names in Ireland, including:

• Aingil Anúabhair: "Proud angels"
• Daoine Uaisle: "The noble folk"
• Daoine maithe: "Good people"
• Deamhan Aerig: "Air demons"
• Dream Anúabhair: "Excessively proud [people]"
• Sídhfir: "Fairy men"
• Sídheógaídhe: "Young Moundlings"
• Slúagh Cille: "Host of the churchyard"
• Slúagh na Marbh: "Host of the dead"
• Slúagh Sídhe: "Mound host"
• Slúagh-Sídhe-Thúatha-Dé-Danann: "Mound host of the Túatha Dé Danann"
• na Uaisle: "The noble" or "The gentry"

Types

The banshee, also called bean sídhe (from Old Irish: ban síde), means "woman of the sídhe." This term now refers to any supernatural woman in Ireland who announces an upcoming death by crying and wailing. In Scottish mythology, her similar figure is the bean sìth (sometimes spelled bean-sìdh). Other beings from the aos sí and daoine sìth groups include the Scottish bean-nighe, a washerwoman who is seen washing bloodstained clothes or armor of someone who will soon die; the leanan sídhe, known as the "fairy lover"; the cat-sìth, a fairy cat; and the cù-sìth, a fairy dog.

The sluagh sídhe, meaning "the fairy host," is sometimes shown in Irish and Scottish stories as a group of flying spirits, possibly cursed, evil, or restless dead. The siabhra (anglicized as "sheevra") may be a type of these lesser spirits, known for causing harm and trouble. However, an Ulster folk song also uses "sheevra" simply to mean "spirit" or "fairy."

Creideamh Sí

Creideamh Sí is the Irish term for "Fairy Faith," a set of beliefs and practices followed by people who want to maintain good relationships with the aos sí and avoid upsetting them. Belief in the Celtic otherworld, the existence of aos sí, and their ability to affect the local area and its people are all parts of Creideamh Sí. It is described as a part of Irish popular religion and exists alongside folk Christianity.

People who believe in these traditions often try to please local aos sí by offering them food and drink. The custom of leaving milk and traditional foods, such as baked goods, apples, or berries, for the aos sí has continued from the time of Christianity until today in some areas of Ireland, Scotland, and among people who live outside these regions. Those who still believe in the aos sí also take care to leave their sacred places untouched and protect them from harm caused by roads or buildings.