Origin: Germanic Old English suffix
Twelfth night has 2 different meanings across 2 categories:
eve of Twelfth day; evening of January 5
A Christian festival marking the coming of Epiphany and concluding the Twelve Days of Christmas, traditionally falling on the evening of January 5 (i.e., on the eve of Twelfth Day, January 6), but also sometimes defined as falling on the evening of January 6 (i.e., on the evening of Twelfth Day itself).