Thankshallowistmas Share definition Flag A merged holiday including Halloween, Thanksgiving, and Christmas, coined under Bill Maher's "New Rules." Thankshallowistmas - now you only have to gather with your batshit family once a year. Thankshallowistmas by Balfdor November 25, 2007 Word of the Day on November 26, 2008 Get the Thankshallowistmas mug.