Someone acting insane like an animal or ghost. Such as screaming, running, or just acting completely idiotic and fake.
That girl Libby is the biggest banchee I have ever seen, all she does is run down the hallways screaming and sticking her butt out like she is cute. She is annoying, don't you hate her? I heard she make her voice sound like that because she thinks it is cute. F.Y.I it isn't!
A word used to describe reckless, primitive yet insightful BADASS. These types of people usually posses the natural instincts of a Native American and act in the manner of an outlaw. It is not uncommon that you might find a banchee orchestrating illegal activities and/or putting their life in danger to seek enjoyment. Their pleasure resides in highs from natural drugs and the adrenalin rushes they obtain from their recklessness. Banchees are very in touch with their inner spirit and love being outdoors. Never mistake a banchee for a hoodlum unless you wish to be scalped on the spot. :)
That dude that disappeared for a month with nothing but a tie dye bandana, Birkenstocks, and a smile on his face is a banchee!