Halloween, Hallowe'en, Allhallows Eve(noun)

the evening before All Saints' Day; often devoted to pranks played by young people

Hallowe'en

the eve of All Saints' Day, 31st October, which it was customary, in Scotland particularly, to observe with ceremonies of a superstitious character, presumed to have the power of eliciting certain interesting secrets of fate from wizard spirits of the earth and air, allowed, as believed, in that brief space, to rove about and be accessible to the influence of the charms employed.