In politics, a diet is a formal deliberative assembly. The term is mainly used historically for the Imperial Diet, the general assembly of the Imperial Estates of the Holy Roman Empire, and for the legislative bodies of certain countries. Modern usage mainly relates to the Japanese Parliament, called "Diet" in English.
The term (also in the nutritional sense) is derived from Medieval Latin dieta, meaning both "parliamentary assembly" and "daily food allowance", from earlier Latin diaeta transcribing Classical Greek δίαιτα diaita, meaning "way of living", and hence also "diet", "regular (daily) work".
Through a false etymology, reflected in the spelling change replacing ae by e, the word came to be associated with Latin dies, "day". The word came to be used in the sense of "an assembly" because of its use for the work of an assembly meeting on a daily basis, and hence for the assembly itself. The association with dies is reflected in the German language use of Tagung (meeting) and -tag (not only meaning "day", as in Montag—i.e. Monday—but also "parliament", "council", or other law-deliberating chamber, as in Bundestag or Reichstag).
In this sense, it commonly refers to the Imperial Diet assemblies of the Holy Roman Empire:
After the Second Peace of Thorn of 1466, a German language Prussian diet Landtag was held in the lands of Royal Prussia, a province of Poland in personal union with the King of Poland.
The Croatian word for a legislative assembly is sabor (from the verb sabrati se, "to assemble"); in historic contexts it is often translated with "diet" in English, as in "the Diet of Dalmatia" (Dalmatinski sabor), "the Croatian Diet" (Hrvatski sabor), or "the Hungarian-Croatian Diet" (Ugarsko-hrvatski sabor).
The Riksdag of the Estates was the diet of the four estates of Sweden, from the 15th century until 1866. The Diet of Finland was the successor to the Riksdag of the Estates in the Grand Duchy of Finland, from 1809 to 1906.
The Swiss Diet was known as Tagsatzung.
- The Japanese Parliament (the Kokkai) is conventionally called the Diet in English, indicating the heavy Prussian influence on the Meiji Constitution, Japan's first modern written constitution.
- Some universities in the UK and India refer to the period of formal examination and the conclusion of an academic term as an "examination diet".