The Minus Oneth Day of Christmas

Me, musing: Should I call this the Minus Oneth Day of Christmas or the Minus First Day of Christmas? Minus First doesn't sound right. Minus Oneth doesn't look right.

Me, replying to myself: Why don't you call it what it is? The Day Before Christmas?

Me, musing further: The Day Before Christmas? That doesn't fit to the sequence of Minus Eighth, Minus Seventh etc. And shouldn't it be Christmas Eve?

Me, replying to myself: That wouldn't fit the sequence either.

Me, musing: True.

( a long pause, represented by dots ) ....................

Me again, musing: I'll go with Oneth. After all, there's a Zeroth Law of Thermodynamics.

Me: So there is. And Christmas Day is the Zeroth Day of Christmas.

Me, disagreeing with myself: I think you'll find that it's the First Day of Christmas.

Me, definitively: It will be the Zeroth Day Of Christmas, for the sake of my own Equilibrium.