Etymology
Cognate with Saterland Frisian Kristmisse (“Christmas”), West Frisian Krystmis (“Christmas”), Dutch Kerstmis (“Christmas”), German Low German Karstmis (“Christmas”). The noun, adjective, and verb are derived from the proper noun. Adjective etymology 1, adjective sense 1 (“red and green in color”) refers to these colors being traditionally associated with Christmas.
Definitions & examples from Wiktionary (CC BY-SA 3.0).