Halloween (hăl'əwēn', häl'-), Oct. 31, the eve of All Saints' Day, observed with traditional games and customs. The word comes from medieval England's All Hallows' eve (Old Eng. hallow="saint"). However, many of these customs predate Christianity, going back to Celtic practices associated with Nov. 1, which was Samhain (sä'wĭn), the beginning of winter and the Celtic new year. Witches and other evil spirits were believed to roam the earth on this evening, playing tricks on human beings to mark the season of diminishing sunlight. Bonfires were lit, offerings were made of dainty foods and sweets, and people would disguise themselves as one of the roaming spirits, to avoid demonic persecution. Survivals of these early practices can be found in countries of Celtic influence today, such as the United States where children go from door to door in costumes demanding "trick or treat."

Halloween had its origins in the festival of Samhain among the Celts of ancient Britain and Ireland. November 1 was considered the end of the summer period, the date on which the herds were returned from pasture and land tenures were renewed. It was also a time when the souls of those who had died were believed to return to visit their homes. People set bonfires on hilltops for relighting their hearth fires for the winter and to frighten away evil spirits, and they sometimes wore masks and other disguises to avoid being recognized by the ghosts thought to be present. It was in these ways that beings such as witches, hobgoblins, fairies, and demons came to be associated with the day.