When did all hallows eve change to Halloween?

Answer 1

Halloween was called Hallow E'en in Ireland of Celtic times. Halloween evolved from "All Hollows" Eve. It originated from the pagan holiday honoring the dead and celebrating the end of summer and start of winter

Answer 2

Halloween is a corruption of the word All Hallows Evening. The next day is All Saints Day. The night before is the evening before. Allhallowe'en, All Hallows' Eve, or All Saints' Eve are the other ways that this became Halloween. The practice of celebrating All Saints Day began in the 8th century.

It is thought to have originated with the ancient Celtic festival of Samhain, when people would light bonfires and wear costumes to ward off roaming ghosts. In the eighth century, Pope Gregory III designated November 1 as a time to honor all saints and martyrs; the holiday, All Saints' Day, incorporated some of the traditions of Samhain