Hallowe'en is a contraction for Hallow's Even(ing), and is another way of saying "the Eve of All Hallows". All Hallows is November 1, All Saints Day.
You see, "Hallow" is an Old English word meaning 'Holy". On November 1, we remember all the Holy people of our history — from Moses to Francis to Teresa of Avila. When we praise the Lord's Prayer, we acknowledge that G–d's name is sacred, set apart, holy.
The word "saint", in turn, is related to the Greek word, "martyr", which means witness. The earliest saints of the church bore witness to their faith by risking torture and death. Later saints bore witness through their actions and words.
And yes, I know Halloween is a borrowing of an older ritual from the Celts. And some people object to it because it's a "pagan" holiday. What these people forget is that "pagan" just means "country-dweller".
So far as first century (C.E.) Romans were concerned, the early Chrisitians were some kind of country bumpkin. Only uneducated rural folk could believe something contrary to the "true religion" of Imperial Rome.
I imagine some modern atheists would agree with the view that a Christian is a type of bumpkin who is willing to accept an infinite number of impossible things before breakfast. Sam Harris and Richard Dawkins seem to subscribe to this view.
I heard a grand story last night that points to a 20th Century witness. I was stuffing envelopes for a local campaign, and was joined by two young girls; one was in fifth grade, the other in ninth. I asked the older girl if she was going to dress for Halloween.
She said, yes; she was dressing as Gandhi, and would give people candy rather than accept it. With the candy, she would hand out cards with quotes from Gandhi's life, such as "Be the change you seek in the world."Within that quote lies the secret of being a saint.