Final answer:
Jingle Bells was a song originally written for Thanksgiving by James Lord Pierpont in 1857 but later became a Christmas staple.
Step-by-step explanation:
The popular Christmas song that was originally written for Thanksgiving is Jingle Bells. Written by James Lord Pierpont in 1857, the song was originally titled One Horse Open Sleigh and was composed for a Thanksgiving church service in Savannah, Georgia. Interestingly, the song quickly became associated with the Christmas holiday season and is now one of the most famous and commonly sung yuletide songs across the world.