The name “Halloween” is an ultra-condensed version of “All Hallow’s Eve.”
According to Merriam-Webster, the name “Halloween” originally comes from All Hallow’s Eve – the second night of a festival called Samhain, dating back to the pagans in Ireland.
“Hallow” comes from an Old English adjective that means “holy,” and “eve” refers to the nighttime setting. All Hallow’s Eve was also referred to as All Hallow’s Even – which was shortened to “Hallow-e’en” by the 16th century.
We eventually dropped the apostrophe and dash in the 18th century, and the rest is history.