An eponym is a person, whether real or fictitious, whose name is thought to be, or has become, synonymous with the name of a particular object or activity.
One of the first cases of eponymity occurred in the second millennium BC, when the Assyrians named each year after a high official (limmu). In ancient Greece, the eponym archon was the highest magistrate in Athens. The Archon of Athens had a yearly charge and each year was named after the elected one (e.g., the year 594 BC was named after Solon). In Rome, the two annual consuls could give different names to the same year.
Both in ancient Greece and independently among the Hebrews, a legendary leader of a tribe gave his name to it (as Achaeus for Achaeans, or Dorus for Dorians). The eponym gave apparent meaning to the mysterious names of tribes, and sometimes, as in the Sons of Noah, provided a primitive attempt at ethnology too, in the genealogical relationships of eponymous originators.
But places and towns too could be given an etymological meaning through an important figure: Peloponnesus was said to derive its name from Pelops. In historical times, new towns have often been named and renamed for historical figures.
The use is today very frequent in science, notably in medicine and in astronomy.
In its correct usage, eponym refers to the person rather than to the object or the word itself. In the latter cases, one would use the adjective eponymic or eponymous. This is a point of frequent confusion, especially because words ending in "-onym" generally refer to the word itself. (e.g., acronyms, homonyms, pseudonyms, ...)
Some books, films, and TV shows are eponymous with their principal character(s): Beavis and Butt-head and Daria, for example.
The term is also applied to music, usually with regard to record titles. For example, Blur's 1997 album was also titled Blur. Many other artists and bands have also released eponymous albums or singles, usually as their debut or second release. (Blur is an oddity in that their eponymous album was their 5th release.) Some bands, such as the Tindersticks, Led Zeppelin, and Weezer, have released more than one. Peter Gabriel's first four long play releases were all such. Another more common term is the self-titled album. The band R.E.M. titled their 1988 compilation CD Eponymous as a joke.
Lists of eponyms
By person's name