The Letter X is a challenging letter for Christmas words, all I could come up with are:
Xmas - An abbreviation for Christmas!
Xbox - One of the most popular gaming consoles; gifted and played over xmas!
There are some awesome Christmas-related words that start wih the Letter Y, here's what I could come up with:
Yorkshire Pudding - A baked batter treat eaten with Xmas dinner in the UK.
Yule Log - This is a large log traditionally burnt on Christmas eve.
Yuletide - This is an archaic term for Christmas, and commonly used in carols.
Youth - Christmas is for all ages, but it's speical for the kids!
The Letter Z is never easy to work with. However, I found some Christmas-related words I think you'll enjoy:
Zazzy - This means shiny or flashy, which is appropriate for Christmas!
Zealous - This means you're showing Zeal.
Zestful - This also means energy or enthusiasm!
Zeal - This means a great burst of energy or enthusiasm.
Zesty - I love this word; it means full of flavor, having a strong spicy flavor, and appealingly piquant or lively. All of which capture the 'zest' of Christmas!