According to King James in his dissertation Daemonologie, the term "faries" was used to describe illusory spirits (demonic entities) that prophesy, consort, and transport individuals they served.
In medieval times, it was believed that a witch or sorcerer who had a compact with a familiar spirit to serve them could receive these types of revelations or use them to perform various tasks.
To the word faie was added the suffix -erie (Modern English -(e)ry), used to express either a place where something is found (fishery, nunnery) or a trade or typical activity engaged in (cookery, thievery).
In later usage it generally applied to any kind of quality or activity associated with a particular type of person, as in English knavery, roguery, wizardry.
Diminutive fairies of one kind or another have been recorded for centuries, but occur alongside the human-sized beings; these have been depicted as ranging in size from very tiny up to the size of a human child.
Nowadays, fairies are often depicted with ordinary insect wings or butterfly wings. Some depictions of fairies depict them wearing some sort of footwear and other depictions of fairies are always barefoot.
The Celtic Revival viewed them as part of Ireland's cultural heritage.
The concept of "fairy" in the narrow sense is unique to English folklore, conflating Germanic elves with influences from Celtic and Romance (French) folklores, and later made "diminutive" according to the tastes of Victorian era "fairy tales" for children.
Fairies have their historical origin in the conflation of Celtic (Breton, Welsh) traditions in the Middle French medieval romances.
The early modern fairies do not have any single origin, representing a conflation of disparate elements of folk belief, influenced by literature and speculation.
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.