Origin of the word Jubilee?

The Levites sound the trumpet of Jubilee (1873 illustration)

Jubilee is an interesting example of a word that evolved to cover two distinct but connected meanings. 

The origin can be traced back to the Old Testament, where the hebrew word yobhel was used to mark the year of the emancipation of slaves. This was to be celebrated every 50th year (Levit. xxv:9); with the sounding of a ram's horn on the Day of Atonement.

In Latin the word combined with iubilare "to shout with joy" (as in jubilant). This added the sense of a celebration, though in the Catholic Church it also became associated with a defined period of repentance brought in by Pope Boniface VIII in 1300.

The particular English form of the celebration was introduced by 'Mad' King George III during the Napoleonic Wars. With the war going badly and the Duke of Wellington AWAL, the intention was to improve national morale. This proved successful, though not alas for King George, who disappeared from public life soon after - the fascinating story is recounted in this The Rest is History podcast.

In the modern era, jubilee is now applied to cover different time periods. Queen Elizabeth II is currently on her third, with Silver (1977) and Platinum (2022) being added to the traditional Golden Jubilee (2002).