Halloween

Where did the name halloween come from? I know it means hallowed evening, but how did it turn into the devilish occurance it is now with a name like that? Where's the connection? And now for some poetry regarding the aforementioned day.

Toddlers is doggie suits
Four-year-olds in cowboy boots
Third grader with an axe
A fifth grader toting a bari sax

What is signified by this procession?
It's a holiday with a candy obssesion
It makes health insurers and parents too
Groan in distress till they turn blue

"There's too much candy" they all say
They all hate it in a passionate way
But it's the holiday of recommendation
From those who work in the dental profession