Wikipedia
Thanksgivukkah is a holiday name portmanteau neologism given to the convergence of the American holiday of Thanksgiving and the first day (and second night) of the Jewish holiday of Hanukkah on Thursday, November 28, 2013. It was the result of a rare coincidence between the lunisolar Hebrew calendar (whose dates reflect both the moon phase and the time of the solar year, and which can have between 353 and 385 days per year) and the Gregorian calendar. Because the calendars are not calculated the same way, Hanukkah appears at a different time each year on the Gregorian calendar.
The term "Thanksgivukkah" was trademarked by Dana Gitell, a Boston-area resident who, along with her sister-in-law, Deborah Gitell, created a Facebook page and a Twitter account devoted to the phenomenon and bought the URL. Boston Magazine reported that the idea was popular all over the U.S.
There has been some disagreement about the name: the Manischewitz company, the country’s top producer of kosher food, has spelled the dual-holiday with one fewer "k" towards the end, as “Thanksgivukah”; and Israeli newspaper Haaretz posed the question: "Why 'Thanksgivukkah'? Why not 'Chanksgiving?'". Haaretz points to a clip from The O.C., the source of the portmanteau " Chrismukkah", as the basis of the "Thanksgivukkah" portmanteau.