the night of 31 October, the eve of All Saints' Day, often celebrated by children dressing up in frightening masks and costumes. Halloween is thought to be associated with the Celtic festival Samhain, when ghosts and spirits were believed to be abroad.
Origin:
late 18th century: contraction of All Hallow Even(see hallow, even2)
Halloween in other Oxford dictionaries
Definition of Halloween in the US English dictionary
