Why is the Diet of Worms not a diet of worms?
Forgive the riddle
The Diet of Worms of 1521 was of course one of the major turning points in the development of Western civilization. It has nothing to do with either food or invertebrates. How come?
The Diet of Worms (Reichstag zu Worms in German) was set up to try Martin Luther (1483 - 1546) for heresy. He did appear there to defend his claims but when he saw the way the wind was blowing he escaped. He was however very popular in his native Saxony and among his fans was his King, Frederick "The Wise". So his King hid him in the old Wartburg castle until the heat had gone off the hunt for him. So Luther became the first Protestant reformer not to lose his head. Giordano Bruno (1548 – 1600), Savonarola (1452 - 1498) and Jan Hus (1369 - 1415) were not so lucky.
So why do we call the Reichstag zu Worms ("National assembly at Worms") the Diet of Worms? The last part is easy. Worms is a German city pronounced as "Vorms", where the "or" is pronounced as the "or" in "horse". The name is ancient and goes back to the Latin. It is just a coincidence that the name also means something in English.
"Diet" is more interesting. The German word "Tag" can mean either "day" or "assembly", perhaps because early assemblies tended to last only one day. But the language of scholarship at the time of the Reichstag zu Worms was Latin. So the Reichstag zu Worms had to be translated into Latin if it was to be discussed at all. And the Latin translators got it wrong. They translated the "Tag" in "Reichstag" as if it meant "day" rather than as if it meant "assembly". And the Latin for "day" is "Dies" (Pronunciation varies but "dee-ayz" is common). So the assembly came to be called a "diet" as a variant of "dies".
And the usage stuck. An important gathering can to this day be called a Diet. The Japanese Diet, for instance is not rice and fish but the Japanese Parliament.
Footnote: I imagine some readers may object to my calling Luther "The first Protestant reformer not to lose his head". What about Wycliffe (1320 - 1384)? It is true that he was a severe critic of the church but he did not create a schism and was saying mass in his church until the end. He died in his bed.
The church would certainly have liked to excommunicate him but, like Luther, he was popular, and people of all ranks, including the monarchy, protected him. Any move against him got howled down. He was a great man.
Another footnote: The mistranslation of "Tag" was not original to the Reichstag zu Worms. The names of much earlier assemblies had also been mistranslated into Latin that way.
And Latin in fact was affected by the mistranslation too. People realized that it was more than a day that was being referred to so a new Latin word -- dieta -- arose in medieval times to mean a public meeting.