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1.
The celebration of Thanksgiving and Christmas with family that will not be able to be together at Christmas.
We will celebrate Thanksmas this year by having Thanksgiving dinner on Thursday, and then by exchanging Christmas presents on Friday.
by The Bergethons November 25, 2008
 
2.
A non-religious holiday observed by friends, not family, who are unable to be together for either Thanksgiving or Christmas; unofficially observed the second Saturday following Thanksgiving but can be held anytime during the holiday season.

The Thanksmas celebration usually consists of a meal with said friends followed by a period of socialization.
Steve: Are we going bowling this Saturday?

Mike: Sorry man, Kate and Andy are having Thanksmas this Saturday, you're welcome to come along!

Steve: Is it Thanksmas already!? Sure!
by Aretelio November 25, 2009
 
3.
the holiday that begins around halloween, and continues on till the end of the year. -it is made up of two phases, the first phase is devoted to more earthly pursuits, while the second revolves around the more spiritual. the second phase now has morphed from worship of a deity and the spiritual, to worship of currency and earthly goods.
when i hear sleigh bells in mid-october and the advertisers are salivating. i know its' time to celebrate the glory that is thanksmas!
by michael foolsley November 23, 2009