Doomed, supernatural, being in unnaturally high spirit, whimsical or strange manner.
Dated back to the 800’s, the adjective fey traveled through England and Scotland acquiring new meanings. In Old English, the word fæge used to refer to human excited behavior, such that presages death; a person on a death wish, fated, destined to die. However, it was also used to describe thoughtless and reckless behavior and not too long after the word shifted its’ meaning to describe timid behavior that endangers its doer. Upon reaching Scotland, the meaning shifted again, this time to represent a person obtaining and displaying unearthly qualities, somewhat mind-distorted, slightly insane.
Although its use wasn’t too positive, nowadays this adjective mainly refers to whimsical, strange or otherworldly qualities of a person.
Why this word?
Personally, I love specific words; words entailing many meanings derived from different histories, words that command you to think and be extremely precise when using them, otherwise it would be misused. Fey is definitely one of these words.
How to use fey?
Fey is an adjective with which you can describe manner, behavior and attitude or people in general.
In the British sense you would use this word to describe a person who is doomed, fated and destined to die: the fact of his survival today doesn’t not change him being fey.
In the Scottish sense, you would use this word to describe a malevolent person, acting as if under spell marked by calamity or evil: the fey look in her eyes made him shiver as he was kissing her.
In the modern American sense, you would normally use it do describe somewhat otherworldly people, whose attitudes and manners can not be explained: he is a strange child with a mysterious smile and a fey manner.