While the various names of this asrchtiectural oddity are given, one is left in the dark as to the origin of names: why is it called a witch window?

Here is my theory: Centuries ago when belief in witches was rampant, there were many expressions using "witch" as a meaning of contempt, or as an explanation of something that went wrong. In modern English, esp. in the US, the word "bitch" is similarly used. So, in framing a house the additional and difficult work of framing an opening for that placement of a window, could have been referred to as a witch of a job, etc.

Also, such a window might have been a good place to hang witches' balls, which were globes of colored glass thought to keep witches away.