Identifying Samhain as a Celtic Death God is one of the most tenacious errors associated with Halloween.
Almost all stories about the origin of Halloween correctly state that Halloween had its origins among the ancient Celts and is based on their "Feast of Samhain." But many conservative Christian authors which are critical of Halloween, Druidism, and/or Wicca have stated that Samhain was named after the famous Celtic "God of the Dead." No such God ever existed. By the late 1990's many secular sources such as newspapers and television programs had picked up the error and propagated it widely. It is now a nearly universal belief, particularly among conservative Protestants.
Modern-day Samhain is the day when many Wiccans believe that their God dies, later to be reborn. [Wicca is a Neo-pagan, Earth-centered religion.] Thus, Samhain is not a God of death; it is actually a yearly observance of the death of a God.

Was/is Samhain a Celtic God?
The answer is a definite yes and no:
YES. He did exist. Many Neopagan and secular sources are probably wrong. As As Isaac Bonewits writes: "Major dictionaries of Celtic Languages don't mention any 'Samhain' deity..." 8 However, there is some evidence that there really was an obscure, little known character named Samain or Sawan who played the role of a very minor hero in Celtic mythology. His main claim to fame was that Balor of the Evil Eye stole his magical cow. His existence is little known, even among Celtic historians. He was a hero, not a god.
NO. Many conservative Christian and secular sources are definitely wrong; there is/was no Celtic God of the Dead. The Great God Samhain appears to have been invented in the 18th century, as a God of the Dead before the ancient Celtic people and their religion were studied by historians and archaeologists.  

McBain's Etymological Dictionary of the Gaelic Language says that 'samhuinn' (the Scots Gaelic spelling) means 'summer's end'..." The Celts observed only two seasons of the year: summer and winter. So, Samhain was celebrated at one of the transitions between these seasons.  
Samhain is pronounced "sah-van", although many neo-Pagans pronounce it as "sow-in" (where "ow" rhymes with "cow"). Samhain is Irish Gaelic for the month of November. Samhuin is Scottish Gaelic for All Hallows, NOV-1.
A language expert has commented that the "mh" in Samhain and Samhuin "would originally have been pronounced like an "m" made without quite closing your mouth." At the present time, the original pronunciation is still heard. Some tighten it to a "v" sound (typical in the south) or loosen it to a "w" sound (typical in the west and, especially, the north). In "Samhain" the "w" pronunciation would be most common." 20
There are many sources supporting the conclusion that Samhain refers to the festival, not a God of the Dead. They come from Celtic, Druidic, Irish, and Wiccan individuals and groups:
Wiccan web site "Brightest Blessings" mentions:
"Samhain (October 31), most often recognized as our New Year, is also called Ancestor Night. It represented the final harvest, when the crops were safely stored for the coming Winter. As the veil between the worlds of life and death is thin on this night, we take this time to remember our beloved dead."  
W.J, Bethancourt III has an online essay which traces the God Samhain myth back to the year 1770 when Col. Charles Vallency wrote a 6 volume set of books which attempted to prove that the Irish people once came from Armenia. Samhain as a god was later picked up in a 1827 book by Godfrey Higgins. 9 That book attempted to prove that the Druids originally came from India. The error might have originated in confusion over the name of Samana, an ancient Vedic/Hindu deity. Bethancourt comments:
"With modern research, archaeology and the study of the Indo-European migrations, these conclusions can be seen as the complete errors they were..."
Later, he writes: " 'Samhain' is the name of the holiday. There is no evidence of any god or demon named 'Samhain,' 'Samain,' 'Sam Hane,' or however you want to vary the spelling."  
Rowan Moonstone, a Wiccan, comments:
"I've spent several years trying to trace the "Great God Samhain" and I have YET to find seminal sources for the same. The first reference seems to be from Col. Vallency in the 1700s and then Lady Wilde in her book 'Mystic Charms and Superstitions' advances the 'Samhain, lord of the dead' theory. Vallency, of course was before the work done on Celtic religion in either literature or archaeology." 12  
The Irish English Dictionary, published by the Irish Texts Society, defines Samhain as follows:
"Samhain, All Hallowtide, the feast of the dead in Pagan and Christian times, signalizing the close of harvest and the initiation of the winter season, lasting till May, during which troops (esp. the Fiann) were quartered." 13
The Scottish Gaelis Dictionary similarly defines Samhain as:
"Hallowtide. The Feast of All Soula. Sam + Fuin = end of summer." 14
J.C. Cooper, author of The Dictionary of Festivals identifies Samhain as:

"Samhain or Samhuinn: (Celtic). 31 October, Eve of 1 November, was the beginning of the Celtic year, the beginning of the season of cold, dearth and darkness." 19
Wiccans have attempted to reconstruct the ancient Celtic religion. They include this festival as one of their 8 Sabbats (seasonal days of celebration). They do not acknowledge the existence of a God of the Dead named Samhain or a similar deity by any other name. Modern-day Druids and other Neopagans also celebrate Samhain as a special day.  


Meaning of Samhain according to most conservative Christians:
The belief that Samhain is a Celtic God of the Dead is near universal among conservative Christian ministries, authors and web sites. They rarely cite references. This is unfortunate, because it would greatly simplify the job of tracing the myth of Samhain as a God back to its origin:
In 1989, Johanna Michaelsen wrote a book opposing the New Age, Humanism and Wicca. It is titled "Your Child and the Occult" 4 She writes:
"The Feast of Samhain was a fearsome night, a dreaded night, a night in which great bonfires were lit to Samana the Lord of Death, the dark Aryan god who was known as the Grim Reaper, the leader of the ancestral Ghosts."
The Watchman Fellowship Inc is a conservative Christian counter-cult group which attempts to raise public concern over religious groups whose theological teachings deviate from orthodox Christianity. Lately, they have also been expressing concern about the dangers of inter-religious dialog. They seem to imply that belief in Baal, a Middle Eastern deity, made it all the way into Celtic lands. They assert:
"It [Halloween] was at this time of the year that Baal, the Celtic god of Spring and Summer, ended his reign. It was also when the Lord of the Dead, Samhain, began his reign."
David Berkowitz, the Son of Sam serial killer, converted to conservative Christianity after his trial and incarceration. He has claimed that he was simply a lookout for an evil Satanic cult who actually performed the murders. He further states that "Sam" in "Son of Sam" comes from the name of the Celtic God of the Dead, Samhain, which he pronounced "Sam-hane." His story is suspect because:  He mispronounced Samhain.
Samhain is not a Celtic God.
Samhain is not a Satanic deity either.
The police investigators are convinced that he was a lone killer, not a member of a group.


David Porter, author of "Hallowe'en: Treat or Trick?," comments:

"The Celtic New Year festival was known as the celebration of Samhain, the Lord of the Dead."
The "Exposing Satanism" website states:

"Halloween, All saints day, All hallows eve or All souls day is [sic] a festival. It was held to honor the Samhain the so called "lord of death". It was a Druidical belief that on the eve of this festival Samhain, lord of death, called together the wicked spirits that within the past 12 months had been condemned to inhabit the bodies of animals." 21
John Ankerbert & John Weldon have written a series of pamphlets that are among the best works by conservative Christian authors for the general public. They make extensive use of footnotes and exhibit careful research of their topic. 17 Apparently they were faced with a conflict with respect to Samhain - whether:  to follow the findings of historians and archaeologists, and admit that Samhain is simply the name of the festival, or
to support previous Christian authors and refer to Samhain as the Druidic God of the Dead even though there is no archaeological evidence to support that conclusion.

They compromised by stating:

"...400 names of Celtic gods are known...'Samhain' as the specific name of the Lord of Death is uncertain, but it is possible that the Lord of Death was the chief druidic deity. We'll follow the lead of several other authors and call him Samhain."
This is a strange comment, because they must have been aware that there is no mention in the historical record of a major Celtic God called Samhain. Thus is it most improbable that Samhain would be the chief Druidic deity, and have gone so long undetected.
On the other hand there are conservative Christians who follow the lead of archaeological and religious research. Richard Bucher from a Massachusetts congregation of the Lutheran church - Missouri Synod writes: 16
"Nothing in the extant literature or in the archaeological finds supports the notion that there ever existed a god of the dead known as Samam (sometimes spelled, 'Samhain,' pronounced 'sow -en'), though hundreds of gods' names are known. Rather, Saman or Samhain is the name of the festival itself. It means "summer's end" and merely referred to the end of one year and the beginning of the new.

This misinformation is caused by numerous conservative Protestant writers copying material from other conservative Protestant writers, without first checking its validity.

Meaning of Samhain according to secular sources:
Most newspapers and other secular sources appear to be following conservative Christian thought, rather than academic research. Two examples are:
Lee Carr wrote the text for a web site "Halloweenies...For kids not meanies." 5 She writes:
"Druids would feast and build huge bonfires to celebrate the Sun God, and thank him for the food that the land produced. The next day, November 1st, was the Celtic New Year, and it was believed that on this day the souls of all dead people would gather together. Therefore, on Halloween, the Celts would also honor the God of the Dead, Samhain."
Scottish Radiance writes about Samhain: 7
"The Celtics believed, that during the winter, the sun god was taken prisoner by Samhain, the Lord of the Dead and Prince of Darkness...On the eve before their new year (October 31), it was believed that Samhain called together all the dead people."

Gods named Sam...:
There appear to be many, mostly male, deities which had names starting with "Sam." None were Celtic. However, the similarity in their names to Samhain might have contributed to the confusion:
Samael was a name in Hebrew for an accuser and a member of God's inner council in charge of dirty deeds
Samana, "the leveler" is the name of an Aryan God of Death (a.k.a. Yama, Sradhadeva, Antaka, or Kritanta) according to the ancient Veda scriptures of Hinduism.
Samas was the Sun God of the northern Semites
Sams was the Sun Goddess of southern Semites
Shamash was the Sun God and God of righteousness, law and divination of the Assyrians and Babylonians


Another Celtic "God": Muck Olla
"Muck Olla" surfaces in some conservative Christian sources as an alleged "early Druid [sic] deity." 10 Another web site refers to Muck Olla as a Celtic sun god. 15 Muck (if we can be so familiar as to refer to a God by his first name) is in reality a type of mythical boogie-man from Yorkshire in England. His name is grounded in old folk stories; he never existed as a Druidic God.