A fairy (also faery, faerie, fay, fae; euphemistically wee folk, good folk, people of peace, fair folk, etc.) is a type of mythical being or legendary creature, a form of spirit, often described as metaphysical, supernatural or preternatural.
Fairies resemble various beings of other mythologies, though even folklore that uses the term fairy offers many definitions. Sometimes the term describes any magical creature, including goblins or gnomes: at other times, the term only describes a specific type of more ethereal creature.
Fairies are generally described as human in appearance and having magical powers. Their origins are less clear in the folklore, being variously dead, or some form of demon, or a species completely independent of humans or angels. Folklorists have suggested that their actual origin lies in a conquered race living in hiding, or in religious beliefs that lost currency with the advent of Christianity. These explanations are not necessarily incompatible, and they may be traceable to multiple sources.
Much of the folklore about fairies revolves around protection from their malice, by such means as cold iron (iron is like poison to fairies, and they will not go near it) or charms of rowan and herbs, or avoiding offense by shunning locations known to be theirs. In particular, folklore describes how to prevent the fairies from stealing babies and substituting changelings, and abducting older people as well. Many folktales are told of fairies, and they appear as characters in stories from medieval tales of chivalry, to Victorian fairy tales, and up to the present day in modern literature.
The word fairy derives from Middle English faierie (also fayerye, feirie, fairie), a direct borrowing from Old French faerie (Modern French féerie) meaning the land, realm, or characteristic activity (i.e. enchantment) of the legendary people of folklore and romance called (in Old French) faie or fee (Modern French fée). This derived ultimately from Late Latin fata (one of the personified Fates, hence a guardian or tutelary spirit, hence a spirit in general); cf. Italian fata, Portuguese fada, Spanish hada of the same origin.
Fata, although it became a feminine noun in the Romance languages, was originally the neuter plural ("the Fates") of fatum, past participle of the verb fari to speak, hence "thing spoken, decision, decree" or "prophetic declaration, prediction", hence "destiny, fate". It was used as the equivalent of the Greek Μοῖραι Moirai, the personified Fates who determined the course and ending of human life.
To the word faie was added the suffix -erie (Modern English -(e)ry), used to express either a place where something is found (fishery, heronry, nunnery) or a trade or typical activity engaged in by a person (cookery, midwifery, thievery). In later usage it generally applied to any kind of quality or activity associated with a particular sort of person, as in English knavery, roguery, witchery, wizardry.
Faie became Modern English fay "a fairy"; the word is, however, rarely used, although it is well known as part of the name of the legendary sorceress Morgan le Fay of Arthurian legend. Faierie became fairy, but with that spelling now almost exclusively referring to one of the legendary people, with the same meaning as fay. In the sense "land where fairies dwell", the distinctive and archaic spellings Faery and Faerie are often used. Faery is also used in the sense of "a fairy", and the back-formation fae, as an equivalent or substitute for fay is now sometimes seen.
The word fey, originally meaning "fated to die" or "having forebodings of death" (hence "visionary", "mad", and various other derived meanings) is completely unrelated, being from Old English fæge, Proto-Germanic *faigja- and Proto-Indo-European *poikyo-, whereas Latin fata comes from the Indo-European root *bhã- "speak". Due to the identical pronunciation of the two words, "fay" is sometimes misspelled "fey".