Halloween = All Hallow's Eve = Eve of All Saints' Day

"Our Father, who art in heaven, hallowed be thy name..."
Yep - "hallowed" means holy.  So the word Halloween comes from the Catholic holy day of the Solemnity of All Saint's - all the holy people partyin' up in heaven.
It all makes sense really when you learn about the feast day - unfortunately most of the American Halloween experience today has obviously become quite secularized and, well, strange.  But there are still elements of the Catholic roots that still exist.
Take this for example:

Where and what is this, you may be asking.  First, let's point out that during this time of year you see skeletons and bones everywhere.  Well, obviously these are bones, but the interesting thing is where they are located.  This is the inside of a chapel in the Church of All Saints' in the Czech Republic.  The words that are supposed to come to one's mind upon seeing this are: memento mori - remember death.  This is meant to help us remember our mortality and one day we will each stand before Almighty God. It is a reminder that God is God and we are not.  It is an encouragement to live a life of virtue and holiness; to live and love well because one day we will all look like that guy in the picture.  Unless you're really holy, then you might look similar to this:

This is St. Bernadette who entered eternal life in 1879 and still looks like she's just sleeping.   The likelihood that we will look like St. Bernadette 150 years after our deaths is slim, unless, of course, God wills it, but the reality remains that we are all called to holiness.  Death was not meant to be a part of the picture, but because of sin we have brought it upon ourselves.  The Good News, quite literally, though is that Christ came to set us free from the power of death.  "Death is swallowed up in victory. Where, O death, is thy victory? Where, O death, is thy sting?" (1 Cor 15: 54-55)  At the Resurrection, the body and the soul will be reunited to live forever for those who live in Christ.  "But thanks be to God who gives us the victory through our Lord Jesus Christ.  Therefore, my beloved brothers, be firm, steadfast, always fully devoted to the work of the Lord, knowing that in the Lord your labor is not in vain." (1 Cor. 15:  57-58)  As human beings we are made of both body and soul integrally.  Our full humanity will shine forth in glory at the Resurrection when we will no longer be subject to the effects of sin and will live, body and soul, forever in the New Jerusalem, the wedding feast of the Lamb.

Read this Q&A from the Word on Fire blog for more on the Catholic roots of All Hallow's Eve here.