The story
From Wednesbury + unreasonable. Wednesbury refers to the case of Associated Provincial Picture Houses Ltd. v Wednesbury Corporation, in which the Court of Appeal of England and Wales refused to quash a decision by the Wednesbury Corporation to ban children under 15 from entering cinemas on Sundays, and laid down in what cases courts could quash unreasonable administrative decisions.
Etymology from Wiktionary, CC BY-SA 4.0.