A mythological, female, magical creature that flies all night looking for prey. They feed on people's sadness. They kill by screaming in such a high pitch that it breaks glass and the arteries of its victem's body so that they drown in their own blood.
You don't want to be a banshee's prey.
A female spirit in Gaelic folklore believed to presage, by wailing, a death in a family.
Irish Gaelic bean sídhe, woman of the fairies, banshee : bean, woman (from Old Irish ben. See gwen- in Indo-European Roots) + sídhe, fairy (from Old Irish síde, genitive of síd, fairy mound. See sed- in Indo-European Roots).
From Old Irish "ben síde" and modern Irish "bean sídhe"/"bean sí", the word roughly means "woman of the fairies" ("bean": "woman"; "sídhe": "fairy mound"). When a citizen of a village dies, a woman (sometimes known as keener (taken from the Irish Gaelic word "caoin" ("to weep/cry")) would sing a caoineadh (lament); legend has it that, for five great Gaelic families: the O'Gradys, the O'Neills, the O'Briens, the O'Connors, and the Kavanaghs, the lament would be sung by a particular fairy woman.
When the stories were translated into English, a distinction between the "banshee" and the other fairy folk was introduced which does not seem to exist in the original stories in their original language, and the funeral lament became a wail that heralded a death. Hearing the cry of the banshee came to forewarn a death in the family and seeing the banshee would signify one's own death.
Most often, the banshee appears a maiden in white, combing their cascading fair hair with a silver comb (which is likely confused with local mermaid myths), while they are also shown in black or green and wearing a grey cloak.
She may also appear (near a body of water) as a washer-woman, and is seen apparently washing the blood-stained clothes of the ones who are about to die. In this guise she is known as the bean-nighe (washing woman).
She appears outside of the houses of the five oldest Gaelic families (O'Connor, O'Grady, O'Neill, O'Brian, Kavanagh), sobbing and crying through the night to warn the family that death is near for one of them. The wailing of many banshees signifies that death is near for someone of great importance.
The bean-nighe ("washerwoman"), her Scottish counterpart, can be seen by a lake or river, washing the bloodstained clothes of the one who will soon die.
The banshee of Gaelic lore is not an evil spirit at all; she's grieving for the one who is about to die and she's trying to warn the family. She is usually heard rather than seen, but she appears as a woman in a silver-grey cloak (she appears as a girl or young woman, a mature woman, or an old woman), her eyes are red from centuries of weeping, and she often tears at her hair as she bawls all night long.
"I heard a woman crying across the fields that night, and death took my grandmother. I knew then that I heard the banshee."
2. Contemporary usage and depictions of the Banshee give her a much more evil nature, being often used as a foe in series and video games, and characterized by her powerful and strident voice.
3. An obnoxious, loud woman.
2. "When a simple mortal hears a Banshee's cry, they die. But Banshees are former witches, and when a witch hears their cry, they turn into a Banshee!" - Charmed
3. Your mother-in-law is a banshee!