Modern christians would have us believe that Halloween has its origins in the Celtic festival of Samhain. The ancient Celts believed that the border between this world and the Otherworld became thin on Samhain, allowing spirits (both harmless and harmful) to pass through. While this is at least partly true, its' true origins are more obscure, mostly because the modern catholic church has spent hundreds of years suppressing the truth. I ask the reader to read the following with an open mind, for the knowledge I am about to impart might, if not properly addressed by a sober and enlightened mind, trigger the sorts of crude humor and crass reactions the adolescent mind is rightly infamous for - something to be avoided at all costs.
Before we treat the main thrust of our narrative, it is important to note the catholic habit of parading bits of holy personages around, or of keeping them secure in holy boxes built expressly for that purpose. Such boxes, elaborately decorated and made from the finest materials, are called reliquaries. The catholic world abounds in such reliquaries. One cannot enter even the humblest of catholic churches without encountering the coccyx of St. Anne, the jawbone of St. Dennis, the knuckle of St. Dominic and so on and so forth. In the dim recesses of our past, virtually no part of sacred anatomy was off limits, and this salient fact leads us directly to the task at hand - explaining the origins of halloween.
Jesus of Nazareth was crucified and entombed. The location of his tomb is known as is the place of his crucifixion. Widely known at one time, but suppressed by the catholic church in medieval times, Jesus suffered an additional and rather ignomious indignity among all the others suffered on the cross, for the same spear that so cruelly pierced his side, also removed his manhood, which was caught along with his blood in a vessel that came to be known as the holy grail. In true catholic fashion, the holy appendage was embalmed, preserved, and placed in a holy reliquary, to be venerated as one would expect of such an object. Samhain at the time was still celebrated widely in the celtic world, and again, in true catholic fashion, another holiday was substituted for the traditional pagan celebrations, only at the time, all the important christian iconic events had already been used up. Local festivals centering on the display of local reliquaries, and sometimes involving travel of the same - albeit under heavy guard, provided the solution.
In short, the solution was the invention of Halloween, which as you have no doubt rightly guessed, was originally known as "Hallowed Wienier," shortened over time to "Hallow Wienie", to "Hallow Ween" and finally "Halloween". The more knowledgeable among you (which clearly excludes the actual faithful, who are routinely ignorant of their history and the tenets of their religion) will no doubt spot the problem. "Aha!" I hear you saying "Weenie is a MODERN term for penis, and therefore this story is clearly fallacious." I anticipated this reaction, and am prepared to address it. So now my friends, it is time - as they say - for the rest of the story.
The vernacular term "weenie" referring to a penis, comes from the term for a sausage of Austrian origin. As all know, the city of Vienna, is known in German as "Wien" (pronounced Ween). A Wiener, therefore is a sausage that comes from Vienna, literally a Vienna style sausage. The "Wiener" is very similar to the modern American sausage of the same name, and it is from this sausage that the term "weenie" originates.
The city of Vienna was founded by the Celts in about 500 BC, and was known by several names before being named Wien. The Romans for instance called it Vindabona. I wrote earlier of the christian habit of venerating holy appendages and body parts. Well, in about 343 AD, the holy penis of Christ made just such a trip, ending up in the city still called Vindabona, but in the throes of adjusting to its new Germanic overlords (see Germanic invasions of Europe for a broader treatment of this). Now, this is not common knowledge, but the Hebrew term for a penis is W-N. Hebrew does not have vowels, so the consonants must be assumed or known, but in short the term is commonly pronounced - you guessed it - "ween."
The christian church, fervent is its desire to supplant the older pagan Celtic holidays (that were still rampant in Celtic Vindabona depite its Roman and Germanic veneers) dispatched the holy "ween" to Vindabona, where it was received with great pomp and veremony. Vindabona's new German overlords, eager to secure the approval and patronage of the weakened, but still powerful and culturally dominant Rome, adopted christianity, named their new capitol "Wien" in honor of the holy relic, and kept the reliquary for many years in the city's old cathedral.
Ironies abound in this story of course, the most obvious being that the corrupted slang "weenie" is in fact very nearly the correct usage of the old Hebrew term, so the term has come full circle.
As for the holy W-N itself, it disappeared during the violent suppression of the Knights Templar in 1307, and has not been seen again.
And now you know, the rest of the story.