Etymology
Irish samhain is from Old Irish samain, samuin, samfuin, referring to 1 November (lathe na samna, "samhain day"), & a festival and royal assembly at that date inside mediaeval Ireland (oenaig na samna, "samhain night"). Its meaning is glossed when "summer's end", & a frequent spelling by having f suggests analysis by popular etymology as sam "summer" & fuin "sunset, end". Old Irish sam "summer" is from either PIE *semo- , cognates are Welsh haf, Breton hañv, Old Norse language sumar all meaning "summer", & Sanskrit sáma "season".

W. Stokes around KZ 40:245 (1907) suggests an etymology from Proto-Celtic *samani by using the pregnant "assembly", cognate to Sanskrit sámana, Gothic samana). Compare to this cetemain "1 May, beltane", related to Middle Welsh kyntefin "1 May, calan haf, May" from *kintu-samino- "beginning of summer" (G. Potato inside Early Irish Lyrics 52), mehefin "June, middle of summer". J. Vendryes inside ''Lexique Étymologique first state l'Irlandais Ancien (1959) concludes that these words containing *semo- "summer" are unrelated to samain, remarking that what is more a Celtic "end of summer" wwhen around July, non November, as evidenced by Welsh gorffennaf "July".

I would so exist as treating by using an Insular Celtic word for "assembly", *samani or *samoni, & the word for "summer", saminos from either *samo- "summer" (alongside samrad < *samo-roto-). Irish samain would be etymologically unrelated to "summer", and derive from "assembly". But note that the name of the month is of Proto-Celtic age, c.f. Gaulish SAMON[IOS] from the Coligny calendar, and the association with "summer" by popular etymology may therefore in principle date to even pre-Insular Celtic times.

Confusingly, Gaulish Samonios (October/November lunation) corresponds to GIAMONIOS, the seventh month (the April/May lunation) and the beginning of the summer season. Giamonios, the beginning of the summer season, is clearly related to the word for winter, PIE *g'hei-men- (Latin hiems, Slavic zima, Greek kheimon, Hittite gimmanza), c. f. Old Irish gem-adaig'' "winter's night" (the vocalism of gam "winter" is influenced by sam, Thurneysen KZ 61:253). It appears, therefore, that for some reason already in Proto-Celtic the first month of the summer season was named "wintry", and the first month of the winter half-year "summery", possibly by ellipsis, "[month at the end] of summer/winter", so that samfuin would be a restitution of the original meaning after all. This interpretation would either invalidate the "assembly" explanation given above, or push back the time of the re-interpretation by popular etymology to very early times indeed.

Bealtaine, Lúnasa and Samhain are still today the names of the months of May, August and November in the Irish language. Similarly, Lùnasdal and Samhain are the modern Scots Gaelic names for August and November.

Ancient Celts
The Celtic calendar divided the year into two halves, the "dark" half, beginning with the month Samonios (the October/November lunation), and the "light half", beginning with the Giamonios (the April/May lunation). The entire year appears to have been considered as beginning with the "dark" half, so that the beginning of Samonios may be considered the Celtic New Year's day. All months began at full moon, and the celebration of New Year took place during the "three nights of Samonios" (Gaulish trinux[tion] samo[nii]), the full moon of nearest 1st November. Likewise, the beginning of the summer season was celebrated at the full moon nearest 1st May (see Beltane). The full moons marking the middle of each half-year may also have been specific festivals, the Coligny calendar marks the mid-summer one (see Lughnasadh), but omits the mid-winter one (see Imbolc). Note that the seasons are not oriented at the solar year, viz. solstice and equinox, but that the mid-summer festival would be considerable later than summer solstice, around 1 August. It appears that the calendar was design to align the lunations with the agricultural cycle of vegetation, and that the actual movements of the Sun were less important.

In medieval Ireland, samain remained the principal festival, celebrated with a great assembly at the royal court in Tara, lasting for three days, consistent with the Gaulish testimony.

Celtic folklore

The Samhain celebration survived in several guises as a festival dedicated to the dead. In Ireland and Scotland, the Féile na Marbh, the "festival of the dead" took place on Samhain.

Samhain Eve, in Irish and Scots Gaelic, Oidhche Shamhna, is one of the principal festivals of the Celtic calendar, and is thought to fall on or around the 31st of October. It represents the final harvest. In modern Ireland and Scotland, the name by which Halloween is known in the Gaelic language is still "Oíche/Oidhche Shamhna".

Bonfires played a large part in the festivities. Even into Christian times, villagers cast the bones of the slaughtered cattle upon the flames, cattle having a prominent place in the pre-Christian Gaelic world. The English word 'bonfire' derives from these "bone fires," but the Gaelic has no such parallel. With the bonfire ablaze, the villagers extinguished all other fires. Each family then solemnly lit its hearth from the common flame, thus bonding the families of the village together.

According to Irish mythology, when you took that nighttime a outstanding shield of Scathach was lowered, allowing a barriers between a worlds to fade & a forces of chaos to invade a realms of the correct sequence, the material globe conjoining by using the world of the dead. At this period a spirits of a dead & people however to exist as innate walked amongst the dwelling. A dead may link to to the web pages in which it got lived & food & amusement were provided in their honour. In a iii years past Samhain, the Sun God Lugh, maimed at Lughnassadh (August 1), dies by the hand of his Tánaiste (counterpart or even heir), a Lord of Misrule. Lugh traverses a boundaries of the worlds on the number 1 day of Samhain. His Tanist occurs as miser &, though shining bright in a wintertime skies, he gives there are no warmth & doesn't temper the breath of the Witch, Cailleach Bheare, the north wind.

Within area of american Brittany Samhain is still heralded per baking of kornigou, cakes baked in the shape of antlers to commemorate the god of winter shedding his "cuckold" horns as he is restored to his kingdom in the Otherworld.

A Romans identified Samhain with their have feast of a dead, the Lemuria. This, all the same, was found in the times initiate to Can 13.

By owning Christianization, a festival inside November (non the Roman festival around Might) became All Hallows' Day on November 1st followed by All Souls' Day, on November 2nd, after which a nighttime of October 31 was called Whole Hallow's Eve, & a remnants festival dedicated to a dead yet morphed into the secular holiday known as Halloween.

Neo-Paganism
Samhain is one of a eight solar holidays or even sabbats of Neopaganism. These are celebrated in the northern hemisphere on October 31 or November 1 and in the southern hemisphere on May 1.

A holiday, by using Beltane, is one of the virtually all popular among Neopagans, & public Samhain rituals invariably attract big gatherings. These are a survive of the harvest festivals (after Lammas and Mabon); in a select few traditions it symbolizes a demise of the old god.

Among a sabbats, these are preceded by Mabon and followed by Yule.

From either an astrological perspective, a setting of Pleiades, the wintertime stars, heralds a mastery of nighttime on top day and the begin of the dark half of the month that is ruled per realms of the moon.

Pop culture references
Samhain is also the title of a Glenn Danzig-fronted band that formed after a dissolution of the Misfits Samhain is the title of the Host-based intrusion detection system [http://la-samhna.de/samhain/ Samhain Labs] Samhain is the title of an experimental & famed computer worm Samhain was a on line-budget horror moving picture according to the legend of Alexander "Sawney" Bean Samhain is the title of the Lord of the Dead inside King's Quest VI who presides over the Realm of the Dead Samhain is the title of the revenant villain in The Real Ghostbusters